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Metabolismus[Bearbeiten | Quelltext bearbeiten]

Acetogenese ist fertig, nun geht's hier Membran gebundene Pyrophosphatasen

1[1]

Membrangebundene Energie konservierende mPPasen und vPPasen[Bearbeiten | Quelltext bearbeiten]

Chemiosmotische Funktion[Bearbeiten | Quelltext bearbeiten]

Die Membran gebundenen Pyrophosphatasen (mPPasen und vPPasen) unterscheiden sich nicht nur strukturell, sondern noch mehr funktionell von den im Cytosol gelösten Pyrophosphat hydrolysierenden cPPasen. Sie koppeln die Hydrolyse von PPi an den Export von H+ oder Na+ - Kationen aus dem Cytosol durch eine Membran: 

PPi + Kation+innen + H2O ⇌ 2 Pi + Kation+außen

Die exergone Hydrolyse ist an einen endergonen Vorgang gekoppelt, nämlich an den Transport der Ionen gegen ein Membranpotential. Die darin enthaltene potentielle Energie steigt durch die gekoppelte Hydrolyse. Ein Teil der im Pyrophosphat enthaltenen Energie wird also in dem Membranpotential konserviert.

Die membrangebundenen PPasen dienen nicht nur als Ionenpumpen, denn Prozess ist reversibel. Beim Rückstrom der Kationen wird Pyrophosphat produziert. [1] Diese Rückreaktion ist nach Substratkettenphosphorylierung und ATP-Bildung durch die ATP-Synthasen und der dritte Weg zum Aufbau energiereicher Phosphatbindungen. [2]

Vorkommen[Bearbeiten | Quelltext bearbeiten]

Nachgewiesen wurde die Chemiosmotische Kopplung der Pyrophosphat-Synthese an einen Protonengradienten bereits 1966, als Membranvesikel eines phototrophen Bakteriums der Familie der Rhodospirillaceae Phosphat zu Pyrophosphat umsetzten.[3] Eine durch ein Membranpotential ermöglichte Synthese einer energiereichen Phosphatverbindung war damals nur von der ATP-Synthase bekannt, die allerdings eine völlig andere Struktur als die PPase aufweist.[4] Allerdings gibt es bei Rhodospirillum offenbar noch einen funktionellen Unterschied zur ATP-Synthase, denn seine PPase ist primär nicht wie jene in der Zellmembran, sondern in der Membran der Acidocalcisomen (saure Polyphosphat - haltige Organellen[5]) angesiedelt.[6]

Membranständige PPasen sind bei 25% aller Prokaryoten nachgewiesen. Bei Pilzen und mehrzelligen Tieren scheinen sie dagegen nicht vor zu kommen. [7] Eine wesentliche Rolle spielen sie als vPPasen bei tierischen Einzellern wie dem Krankheitserreger Trypanosoma brucei, einzelligen Algen und insbesondere bei allen Landpflanzen. Sie sind bei Organismen besonders verbreitet, die regelmäßig unter Energie-, Sauerstoffmangel, Salz- und anderen Stressbedingungen leiden. [1]

Evolution[Bearbeiten | Quelltext bearbeiten]

Die mPPasen und vPPasen haben einen prinzipiell gleichen Aufbau und eine gemeinsame evolutionäre Wurzel, die wohl bis zum Urvorfahr aller Lebewesen zurückreicht. Es wird auch vermutet, dass sie aus einer Phase der chemischen Evolution stammen, als abiotisch entstandenes Pyrophosphat vielleicht die zentrale Rolle als Energieüberträger für die Bildung von Nukleinsäuren spielte.[8] [9] [10]

Die erste membranständige PPase hat vermutlich Na+ transportiert. [7] [11] Das legt die vergleichende Untersuchung der Aminosäurensequenzen dieser Enzyme nahe. Zur selben Vermutung, nämlich dass Na+-Pumpen den H+-Pumpen vorausgingen, kam man auch bei den ATP-Synthasen.[12] Biomembrane sind generell leichter für H+-Ionen zu durchdringen als für Na+, und so erforderte es eine ganze Zeit der Coevolution von Membranproteinen und Membranen, bis eine H+-ATP-Synthase funktionieren konnte. [13] [14] Aus den Na+ PPasen haben sich in ihrer weiteren Evolution verschiedene H+-PPasen entwickelt, die zum Teil K+-abhängig sind [11].

Aufbau und Reaktionsmechanismus[Bearbeiten | Quelltext bearbeiten]

Abb. 5. Membranständige vPPase der Mungobohne Vigna radiata[15]

Seit 2012 konnte die genaue Struktur einer pflanzlichen H+-abhängige vPPase und eine davon evolutionär weit entfernte Na+-mPPase des Bakteriums Thermotoga maritima ermittelt werden. Beiden unterscheiden sich im Wesentlichen nicht. Sie bestehen beide aus zwei funktionell gleichen Proteinketten. Diese durchdringen die Membran in 16 Segmenten. Ihr reaktives Zentrum befindet sich auf der Cytosol-Seite etwa 20 Å entfernt von der Membran in einer hydrophilen Trichter-förmigen Struktur. [1]

In Abb. 5 ist eine pflanzliche vPPase schematisch dargestellt. In der Frontansicht ist das dimere Enzym 85 Å breit und 75 Å hoch.

Das reaktive Zentrum liegt auf Seiten des Cytosols (blauer Hintergrund) unterhalb der Membran (weißer Hintergrund). Die hellblauen Spiralen symbolisieren die im Inneren liegenden Proteinsegmente. Sie bieten nach der Cytosolseite hin einen hydrophilen Zugang zu dem Enzym und oben einen hydrophilen Kanal (roter Pfeil), durch den Ionen die Membran durchdringen können.

Im reaktiven Zentrum sind links die Substrate dargestellt. Pyrophosphat ist mit 4 Mg+-Ionen an das Protein gekoppelt. Das zur Hydrolyse dienende Wasser ist durch zwei Asparaginsäure - Gruppen an das Enzym assoziiert.[16]

Abb. 6. Möglicher Reaktionsmechanismus [17]

In Abb. 6 findet sich ein Arbeitsmodell für die reversible, Ionen transportierende Hydrolyse. Man kann sich den hydrolytischen Weg (in Abb. 6 gegen den Uhrzeigersinn) folgendermaßen vorstellen:

  1. Der Pump-Mechanismus wird dadurch vorbereitet, dass ein Pyrophosphat-Ion im Austausch gegen ein Hydrogenphosphat-Ion in das Reaktionszentrum eindringt. In der PP-Phase ist das Enzym zur cytosolischen Seite geschlossen, aber der Transmembrankanal ist kurz geöffnet.
  2. Synchron mit dem Entweichen des Kations nach Außen findet die Hydrolyse statt. Dabei bewegt sich ein zunächst an die Asparginsäure D287 gebundenes H+ an den Ort D294, an den vorher das Kation gebunden war. Die an D273 zurückbeibende OH--Gruppe ist so nukleophil, dass die nukleophile Substitution[18] zu zwei Hydrogenphosphat-Ionen gelingt (2P in der Abbildung).
  3. In Phase P ist das Enzym nach Austausch des ersten Phosphat-Ions mit einem Hydroxylion OH- unten geöffnet. Es kann ein zu transportierendes Kation eindringen. Danach ist der Zustand wieder hergestellt, in dem das zweite Phosphation gegen Pyrophosphat ersetzt werden kann und ein neuer Zyklus beginnt. [1]

Jeder dieser Schritte ist reversibel. Wenn kaum Pyrophosphat vorhanden ist, steigt die Wahrscheinlichkeit in der P+-Phase, dass das zweite Phosphat nicht ausgetauscht wird. Nach Entweichen des Kations nach innen kann ein zweites Phosphat (im Austausch gegen OH-) in das Enzym eindringen. Eine hohe Kationenkonzentration außen erhöht dann die Chance, dass die Kondensationsreaktion zu Pyrophosphat gelingt.[17]

Mol. Evol:[Bearbeiten | Quelltext bearbeiten]

Die unvermeidliche Reise zum Dasein Michael J. Russell, Wolfgang Nitschke & Elbert Branscomb: The inevitable journey to being. In: Philosophical Transactions of the Royal Society B: Biological. 368. Jahrgang, Nr. 20120254, 2013, doi:10.1098/rstb.2012.0254 (royalsocietypublishing.org [PDF]). Symmetrie-Brechung, Chemiosmosis for free[19]

HGT: (Alejandro 2015)[20] Genome sequencing has revealed that horizontal gene transfer (HGT) is a major evolutionary process in bacteria. Although it is generally assumed that closely related organisms engage in genetic exchange more frequently than distantly related ones, the frequency of HGT among distantly related organisms and the effect of ecological relatedness on the frequency has not been rigorously assessed. Here, we devised a novel bioinformatic pipeline, which minimized the effect of over-representation of specific taxa in the available databases and other limitations of homology-based approaches by analyzing genomes in standardized triplets, to quantify gene exchange between bacterial genomes representing different phyla. Our analysis revealed the existence of networks of genetic exchange between organisms with overlapping ecological niches, with mesophilic anaerobic organisms showing the highest frequency of exchange and engaging in HGT twice as frequently as their aerobic counterparts. Examination of individual cases suggested that inter-phylum HGT is more pronounced than previously thought, affecting up to [sim]16% of the total genes and [sim]35% of the metabolic genes in some genomes (conservative estimation). In contrast, ribosomal and other universal protein-coding genes were subjected to HGT at least 150 times less frequently than genes encoding the most promiscuous metabolic functions (for example, various dehydrogenases and ABC transport systems), suggesting that the species tree based on the former genes may be reliable. These results indicated that the metabolic diversity of microbial communities within most habitats has been largely assembled from preexisting genetic diversity through HGT and that HGT accounts for the functional redundancy among phyla.[1]

last[Bearbeiten | Quelltext bearbeiten]

Membrane-Integral Inorganic Pyrophosphatase in the Genome of an Apparently Pre-LUCA Extremophile [21] before the occurrence of the evolutionary bifurcation into Crenarchaeota and Euryarchaeota

Wirklich vor Luca (Artikel gespeichert)

n the genomes of two very early symbiotic organisms, Ignicoccus hospitalis and Nanoarchaeum equitans, no gene for a miPPase was found

Wurzeln vor LUCA

K+indep H+ separate branches of CKc and C. saccharolyticus R. rubrum (Rr) and Streptomyces coelicolor (Sc) on the other is shown

It has now become of increasing evolutionary actuality, with Na+-translocation apparently preceding H+-translocation (Luoto et al. 2011)

Admiraal:

Phosphorylierung SN1[22]

Nitschle ... & Russel[Bearbeiten | Quelltext bearbeiten]

Metalloenzyme [23]:

Abstract Many metalloenzymes that inject and extract reducing equivalents at the beginning and the end of electron transport chains involved in chemiosmosis are suggested, through phylogenetic analysis, to have been present in the Last Universal Common Ancestor (LUCA). Their active centres are affine with the structures of minerals presumed to contribute to precipitate membranes produced on the mixing of hydrothermal solutions with the Hadean Ocean ~ 4 billion years ago. These mineral precipitates consist of transition element sulphides and oxides such as nickelian mackinawite ([Fe > Ni]2S2), a nickel-bearing greigite (~ FeSS[Fe3NiS4]SSFe), violarite (~ NiSS[Fe2Ni2S4]SSNi), a molybdenum bearing complex (~ MoIV/VI2Fe3S0/2 −9) and green rust or fougerite (~[FeIIFeIII(OH)4]+[OH]−). They may be respectively compared with the active centres of Ni–Fe hydrogenase, carbon monoxide dehydrogenase (CODH), acetyl coenzyme-A synthase (ACS), the complex iron–sulphur molybdoenzyme (CISM) superfamily and methane monooxygenase (MMO). With the look of good catalysts – a suggestion that gathers some support from prebiotic hydrothermal experimentation – and sequestered by short peptides, they could be thought of as the original building blocks of proto-enzyme active centres. This convergence of the makeup of the LUCA-metalloenzymes with mineral structure and composition of hydrothermal precipitates adds credence to the alkaline hydrothermal (chemiosmotic) theory for the emergence of life, specifically to the possibility that the first metabolic pathway – the acetyl CoA pathway – was initially driven from either end, reductively from CO2 to CO and oxidatively and reductively from CH4 through to a methane thiol group, the two entities assembled with the help of a further thiol on a violarite cluster sequestered by peptides. By contrast, the organic coenzymes were entirely a product of the first metabolic pathways. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.


Laura M Barge & M J Russell[2]: Cells use three main ways of generating energy currency to drive metabolism: (i) conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) by the proton motive force through the rotor-stator ATP synthase; (ii) the synthesis of inorganic phosphate∼phosphate bonds via proton (or sodium) pyrophosphate synthase; or (iii) substrate-level phosphorylation through the direct donation from an active phosphoryl donor. A mechanism to produce a pyrophosphate bond as “energy currency” in prebiotic systems is one of the most important considerations for origin of life research. Baltscheffsky (1996) suggests that inorganic pyrophosphate ( P 2 O 7 4 - ; PPi) may have preceded ATP/ADP as an energy storage molecule in earliest life, produced by an H+ pyrophosphatase. Here we test the hypothesis that PPi could be synthesized in inorganic precipitates simulating hydrothermal chimney structures transected by thermal and/or ionic gradients. Appreciable yields of PPi were obtained via substrate phosphorylation by acetyl phosphate within the iron sulfide/silicate precipitates at temperatures expected for an alkaline hydrothermal system.


Huber & Wächtershäuser [24] In experiments modeling the reactions of the reductive acetyl{\textendash}coenzyme A pathway at hydrothermal temperatures, it was found that an aqueous slurry of coprecipitated NiS and FeS converted CO and CH3SH into the activated thioester CH3-CO-SCH3, which hydrolyzed to acetic acid. In the presence of aniline, acetanilide was formed. When NiS-FeS was modified with catalytic amounts of selenium, acetic acid and CH3SH were formed from CO and H2S alone. The reaction can be considered as the primordial initiation reaction for a chemoautotrophic origin of life.

Baltscheffsky, H. "Energy conversion leading to the origin and early evolution of life: did inorganic pyrophosphate precede adenosine triphosphate." Origin and evolution of biological energy conversion. VCH, New York (1996): 1-9. [25]

Holm, Nils G., and Herrick Baltscheffsky. "Links between hydrothermal environments, pyrophosphate, Na+, and early evolution." Origins of Life and Evolution of Biospheres 41.5 (2011): 483-493.[10]

Na+-translocating Membrane Pyrophosphatases (Heidi H. Luoto ea 2011)[Bearbeiten | Quelltext bearbeiten]

Are Widespread in the Microbial World and Evolutionarily Precede H+-translocating Pyrophosphatases [26]

Membrane-bound pyrophosphatases (mPPases) couple pyrophosphate (PPi) hydrolysis to H+ and/or Na+ transport. In the present study, we describe a novel subfamily of H+-transporting mPPases that are only distantly related to known mPPases and show an unusual pattern of regulation by Na+ and K+.

mPPases; Transporter Classification Database number 3.A.10) couple pyrophosphate (PPi) hydrolysis to transmembrane transport of H+, Na+ or both against their electrochemical potential gradients

An mPPase is present in ∼25% of prokaryotic species, many protists and all plants

PPi-powered ion transport system provides the cell with an energy reserve that appears to be particularly physiologically important during various stresses, such as energy restriction or exposure to salinity or toxins [6–10]. mPPases hold significant biotechnological potential because their engineered overexpression significantly increases the stress tolerance of model and agricultural plants [11].

Approximately half of the identified mPPases require K+ ions for maximal activity [1]. K+ binds in the funnel and interacts with the substrate PPi. K+-independent mPPases have a specifically conserved lysine residue,

the ancestral mPPase apparently operated as a Na+ pump (Na+-PPase), three evolutionarily independent lineages from Na+ to H+ transport (H+-PPases) and one to Na+ and H+ co-transport (Na+,H+-PPase) have been identified [16,17].

Na+ 2006 Mulkidjanian[Bearbeiten | Quelltext bearbeiten]

A.Y. Mulkidjanian, K.S. Makarova, M.Y. Galperin, E.V. Koonin Inventing the dynamo machine: the evolution of the F-type and V-type ATPases Nat. Rev. Microbiol., 5 (2007), pp. 892–899[27] :

F-type and V-type reversible ATPases are membrane-associated molecular machines that couple the transfer of protons or sodium cations across the membrane with ATP hydrolysis or synthesis (Fig. 1). These enzymes represent the cornerstone of cellular bioenergetics and are ubiquitous to all three domains of life (bacteria, archaea and eukaryotes). The F-type F0F1 ATPases are found in the mitochondria and chloroplasts of all eukaryotic cells and in most bacteria, and have a range of structural features that distinguish them from the V (vacuolar)-type ATPases. V-type ATPases occur in eukaryotic cytoplasmic membranes (in particular, vacuoles), archaea and in a small, although important, number of bacteria. In rooted phylogenetic trees, eukaryotic, archaeal and bacterial V-type ATPases invariably cluster together, and separately, from the F-type ATPases9. The F-type ATPase is thought to be the ancestral bacterial cation-translocating ATPase, and conversely, the V-type ATPase is thought to be the ancestral archaeal form. Accordingly, the presence of V-type ATPases in several bacterial lineages, and the presence of F-type ATPases in two species of the archaeal genus Methanosarcina, is thought to be a consequence of the extensive horizontal transfer of the respective genes between the two domains.

The rotary proton- and sodium-translocating ATPases are reversible molecular machines present in all cellular life forms that couple ion movement across membranes with ATP hydrolysis or synthesis. Sequence and structural comparisons of F- and V-type ATPases have revealed homology between their catalytic and membrane subunits, but not between the subunits of the central stalk that connects the catalytic and membrane components. Based on this pattern of homology, we propose that these ATPases originated from membrane protein translocases, which, themselves, evolved from RNA translocases. We suggest that in these ancestral translocases, the position of the central stalk was occupied by the translocated polymer.


Stammbaum F/V-ATPase

The presence of essentially identical Na+-binding sites in the membrane-spanning c/K-oligomers of the F- and V-ATPases, combined with the scatter of Na+-dependent ATPases among the more common, H+-dependent ones in both the F and the V branches of the phylogenetic tree, leads to the unexpected conclusion that, during evolution, Na+-driven membrane bioenergetics preceded the proton-based energy conversion that is dominant in modern cells. This conclusion is further buttressed by the substantially greater conductivity of lipid bilayers to protons than to sodium cations and by the existence of distinct mechanisms that make membranes proton-tight in different lineages of cellular life. Under this scenario, the emergence of membrane bioenergetics was constrained by the evolution of the membranes themselves, not only the energy-converting enzymes.


[28]

All living cells routinely expel Na+ ions, maintaining lower concentration of Na+ in the cytoplasm than in the surrounding milieu. In the vast majority of bacteria, as well as in mitochondria and chloroplasts, export of Na+ occurs at the expense of the proton-motive force. Some bacteria, however, possess primary generators of the transmembrane electrochemical gradient of Na+ (sodium-motive force). These primary Na+ pumps have been traditionally seen as adaptations to high external pH or to high temperature. Subsequent studies revealed, however, the mechanisms for primary sodium pumping in a variety of non-extremophiles, such as marine bacteria and certain bacterial pathogens. Further, many alkaliphiles and hyperthermophiles were shown to rely on H+, not Na+, as the coupling ion. We review here the recent progress in understanding the role of sodium-motive force, including (i) the conclusion on evolutionary primacy of the sodium-motive force as energy intermediate, (ii) the mechanisms, evolutionary advantages and limitations of switching from Na+ to H+ as the coupling ion, and (iii) the possible reasons why certain pathogenic bacteria still rely on the sodium-motive force. [29]

== Shih-Ming Lin ==

Membranständige vPPase der Mungobohne Vigna radiata[16]

Crystal structure of a membrane-embedded H+-translocating pyrophosphatase


homodimers in the vacuolar membrane of plants and the plasma membrane of several protozoa and prokaryotes

crystal structure of a Vigna radiata H+-PPase (VrH+-PPase)Mungbohne

16 transmembrane helices. IDP is bound in the cytosolic region of each subunit and trapped by numerous charged residues and five Mg2+

Proton pumping can be initialized by PPi hydrolysis, and H+ is then transported into the vacuolar lumen proton-pumping proteins, vacuolar H+-ATPases (V-ATPases) and H+-PPases, coexist on plant vacuolar membranes and use ATP and PPi, respectively, as energy sources for H+ translocation. a fourth category of primary H+ pump, H+-PPases, was thus determined.

Previous evidence suggests that the dimerization of H+-PPase is important for H+ translocation activity23. However, the possible residues that can be protonated as part of proton conduction could not be found in the dimer interface in VrH+-PPase. The proton-pumping proteins usually use bound water molecules to assist proton transport28; examples are bacteriorhodopsin26 and P-type H+-ATPases29.

Vacuolar[Bearbeiten | Quelltext bearbeiten]

Masayoshi Maeshima[Bearbeiten | Quelltext bearbeiten]

Vacuolar H+-pyrophosphatase[30]

unique, electrogenic proton pump distributed among most land plants, but only some alga, protozoa, bacteria, and archaebacteria. acidifies vacuoles in plant cells,

In addition to the well-known soluble PPases, membrane-bound PPases have recently been discovered in the plant thylakoid membrane [4] and plant mitochondria These membrane-bound PPases, however, did not show proton pump activity.

coupling mechanism between the pyrophosphate hydrolysis and the active proton transport

requirement of Mg2+ and K+.

H+-PPase coexists with H+-ATPase in a single vacuolar membrane

The actual free energy change for PPi hydrolysis in the cytoplasm has been calculated to be 27.3 kJ/mol at pH 7.3 [21]. The H+/PPi stoichiometry of H+-PPase has been determined to be 1, and the steady-state pH generated by the enzyme 3.2

The level of H+-PPase in plants is regulated under stress conditions. Colombo and Cerana [84] have reported an increment of H+-PPase activity in carrot suspension cells with NaCl treatment.

Fuchs[Bearbeiten | Quelltext bearbeiten]

Fuchs[31]

Nutzung von Diphosphat im Stoffwechsel[Bearbeiten | Quelltext bearbeiten]

Yoko 2015Discovery of PPi [32]

Phosphoenolpyruvate carboxykinase (PEPCK) is one of the pivotal enzymes that regulates the carbon flow of the central metabolism by fixing CO2 to phosphoenolpyruvate (PEP) to produce oxaloacetate or vice versa. Whereas ATP- and GTP-type PEPCKs have been well studied, and their protein identities are established, inorganic pyrophosphate (PPi)-type PEPCK (PPi-PEPCK) is poorly characterized. Despite extensive enzymological studies, its protein identity and encoding gene remain unknown. In this study, PPi-PEPCK has been identified for the first time from a eukaryotic human parasite, Entamoeba histolytica, by conventional purification and mass spectrometric identification of the native enzyme, followed by demonstration of its enzymatic activity. A homolog of the amebic PPi-PEPCK from an anaerobic bacterium Propionibacterium freudenreichii subsp. shermanii also exhibited PPi-PEPCK activity. The primary structure of PPi-PEPCK has no similarity to the functional homologs ATP/GTP-PEPCKs and PEP carboxylase, strongly suggesting that PPi-PEPCK arose independently from the other functional homologues and very likely has unique catalytic sites. PPi-PEPCK homologs were found in a variety of bacteria and some eukaryotes but not in archaea. The molecular identification of this long forgotten enzyme shows us the diversity and functional redundancy of enzymes involved in the central metabolism and can help us to understand the central metabolism more deeply. 

PPi + D-Fructose-6-P ⇌ D-Fructose-1,6-bisphosphat
ATP + D-Fructose-6-P → D-Fructose-1,6-bisphosphat

Pyruvate, phosphate dikinase (2.7.9.1) 

PPi + AMP + PEP ⇌ Pi + ATP + Pyruvate
Pi + AMP + PEP ⇌ Pi + ATP + Pyruvate
ADP + PEP ⇌ Pi + ATP + Pyruvate

Phosphoenolpyruvate carboxykinase (EC 4.1.1.38) 

PPi + oxaloacetat ⇌ Pi + PEP + CO2
ATP + oxaloacetat ⇌ ADP + PEP + CO2
Pi + oxaloacetat ← Pi + PEP + CO2

UDP‐glucose pyrophosphorylase: 

UDP-Glucose + PPi ⇌ UTP + Glu-1-P + UTP

Peter Geigenberger: Regulation of sucrose to starch conversion in growing potato tubers. J Exp Bot January 1, 2003 vol. 54 no. 382 457-465

Pyrophosphat bei Pflanzen [33]

but the cytosol of these cells does not contain soluble PPiases, thus permitting an accumulation of a significant amount of PPi (0.2–0.3 mM) (Weiner et al., 1987). This cytosolic PPi can then act as an energy donor for at least three reactions, namely PPi-dependent proton pumping at the level of tonoplast (Maeshima, 2000 and Rea et al., 1992), sucrose degradation via sucrose synthase, UDP-glucose phosphorylase and phosphofructokinase (Stitt, 1990 and Kruger, 1997), and entry into glycolysis via the pyrophosphate fructose-6-phosphate phosphotransferase (Stitt, 1990 and Davies, 1997). These PPi-consuming reactions are ubiquitous in higher plants and operate in parallel with the corresponding ATP-dependent enzymes. Therefore, PPi is now considered an energetic alternative to ATP in plant cells (Stitt, 1998). [34]

Stitt:

Pyrophosphate serves as an alternative energy donor to ATP for sucrose mobilisation via sucrose synthase, for glycolysis via pyrophosphate: fructose-6-phosphate phosphotransferase, and for tonoplast energisation via the tonoplast proton-pumping pyrophosphatase. This review considers the possible roles of these pyrophosphate-driven reactions. Correlative evidence based on expression patterns, the distribution of proteins and activities in various tissues, and comparisons of the in vitro properties of the enzymes with the in vivo metabolite levels indicates an important role in young growing tissues and in stress conditions including anaerobiosis, but interpretation is complicated by the reversibility of the pyrophosphate-driven reactions and by their duplication by ATP-dependent reactions. The review then considers the evidence emerging from experiments using reversed genetics to alter expression of sucrose synthase, the pyrophosphate: fructose-6-phosphate phosphotransferase, and the tonoplast proton-pumping pyrophosphatase. This approach has revealed that sucrose synthase plays an essential role in sucrose breakdown in potato tubers, and that pyrophosphate: fructose-6-phosphate phosphotransferase catalyses a near-equilibrium reaction with a net flux in the direction of glycolysis. However, it does not support a special role of the latter enzymes in stress responses. Interpretation is complicated by compensation, which can include expression of other members of a gene family, use of alternative pathways, and relaxation of the feed back regulation in response to decreased expression of the enzyme. In an alternative approach, ectopic overexpression of soluble pyrophosphatase from E. coli has been used as a tool to decrease the levels of pyrophosphate in the cytosol. Constitutive overexpression leads to dramatic changes in sucrose and starch synthesis, sink-source relations and plant growth, phloem-specific overexpression of soluble pyrophosphatase leads to an inhibition of phloem transport, leaf mesophyll-specific overexpression leads to a small stimulation of sucrose synthesis, and potato tuber-specific overexpression leads to an inhibition of starch accumulation.


The H+-pyrophosphatase of Rhodospirillum rubrum [6]

Einzelnachweise[Bearbeiten | Quelltext bearbeiten]

[35]

  1. ↑ a b c d e Tommi Kajandera, Juho Kellosalob & Adrian Goldman: Inorganic pyrophosphatases: One substrate, three mechanisms. In: FEBS Letters. 587. Jahrgang, Nr. 13, 2013, S. 1863–1869, doi:10.1016/j.febslet.2013.05.003 (sciencedirect.com).
  2. ↑ a b Laura M. Barge, Ivria J. Doloboff, Michael J. Russell, David VanderVelde, Lauren M. White, Galen D. Stucky, Marc M. Baum, John Zeytounian, Richard Kidd, Isik Kanik: Pyrophosphate synthesis in iron mineral films and membranes simulating prebiotic submarine hydrothermal precipitates. In: Geochimica et Cosmochimica Acta. 128. Jahrgang, 2014, S. 42705, doi:10.1016/j.gca.2013.12.006 (sciencedirect.com).
  3. ↑ Herrick Baltscheffsky, Lars-Victor von Stedingk, Hans-Walter Heldt, Martin Klingenberg: Inorganic Pyrophosphate: Formation in Bacterial Photophosphorylation (Inorganic pyrophosphate is identified as the major product of photophosphorylation by isolated chromatophores from Rhodospirillum rubrum in the absence of addded nucleotides.). In: Science. 274. Jahrgang, Nr. 3740, 1966, S. 1120–1122 (jstor.org).
  4. ↑ Jennifer Moyle, Roy Mitchell, Peter Mitchell: Proton-translocating pyrophosphatase of Rhodospirillum rubrum. In: FEBS Letters. 23. Jahrgang, Nr. 2, 1972, S. 233–236, doi:10.1016/0014-5793(72)80349-1 (sciencedirect.com).
  5. ↑ Roberto Docampo , Wanderley de Souza, Kildare Miranda, Peter Rohloff and Silvia N. J. Moreno: Acidocalcisomes? conserved from bacteria to man. In: Nature Reviews Microbiology. 3. Jahrgang, Nr. 3, 2005, S. 251–261, doi:10.1038/nrmicro1097 (nature.com [PDF]).
  6. ↑ a b Manfredo Seufferheld, Christopher R. Lea, Mauricio Vieira, Eric Oldfield, and Roberto Docampo: The H+-pyrophosphatase of Rhodospirillum rubrum is predominantly located in Polyphosphate-rich Acidocalcisomes. In: J. Biol. Chem. 279. Jahrgang, 2004, S. 51193–51202, doi:10.1074/jbc.M406099200.
  7. ↑ a b Heidi H. Luoto, Georgiy A. Belogurov, Alexander A. Baykov, Reijo Lahti, and Anssi M. Malinen: Na+-translocating Membrane Pyrophosphatases Are Widespread in the Microbial World and Evolutionarily Precede H+-translocating Pyrophosphatases. In: J. Biol. Chem. 286. Jahrgang, Nr. 11, 2011, S. 21633–21642, doi:10.1074/jbc.M111.244483.
  8. ↑ Alexander A. Baykov, Anssi M. Malinen, Heidi H. Luoto,Reijo Lahti: Pyrophosphate-Fueled Na+ and H+ Transport in Prokaryotes. In: Microbiol. Mol. Biol. Rev. 77. Jahrgang, Nr. 2, 2013, S. 267–276, doi:10.1128/MMBR.00003-13 (asm.org [PDF]).
  9. ↑ Herrick Baltscheffsky: Origin and evolution of biological energy conversion. Hrsg.: Herrick Baltschefsky und so. John Wiley & Sons,, 1996, Energy conversion leading to the origin and early evolution of life: did inorganic pyrophosphate precede adenosine triphosphate?.
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  11. ↑ Armen Y. Mulkidjanian, Pavel Dibrov, Michael Y. Galperin: The past and present of sodium energetics: May the sodium-motive force be with you. In: Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1777. Jahrgang, Nr. 7-8, 2008, S. 985–992, doi:10.1016/j.bbabio.2008.04.028 (sciencedirect.com).
  12. ↑ Armen Y Mulkidjanian, Michael Y Galperin, Kira S Makarova, Yuri I Wolf and Eugene V Koonin: Evolutionary primacy of sodium bioenergetics. In: Biology Direct. 3. Jahrgang, Nr. 13, 2008, doi:10.1186/1745-6150-3-13 (biomedcentral.com).
  13. ↑ Armen Y Mulkidjanian, Kira S Makarova, Michael Y Galperin, Eugene V Koonin: Inventing the dynamo machine: the evolution of the F-type and V-type ATPases. In: Nature Reviews Microbiology. 5. Jahrgang, Nr. 11, 2007, S. 892–899, doi:10.1038/nrmicro1767 (nature.com [PDF]).
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  15. ↑ a b Shih-Ming Lin, Jia-Yin Tsai, Chwan-Deng Hsiao, Yun-Tzu Huang, Chen-Liang Chiu, Mu-Hsuan Liu, Jung-Yu Tung, Tseng-Huang Liu, Rong-Long Pan & Yuh-Ju Sun: Crystal structure of a membrane-embedded H+-translocating pyrophosphatase. In: Nature. 484. Jahrgang, Nr. 7394, 2012, S. 399–403, doi:10.1038/nature10963 (nature.com). Grafik:working model for proton pumping in VrH+-PPase A working model for proton pumping in VrH+-PPase
  16. ↑ a b Juho Kellosalo, Tommi Kajander, Konstantin Kogan, Kisun Pokharel, Adrian Goldman: The Structure and Catalytic Cycle of a Sodium-Pumping Pyrophosphatase. In: Science. 337. Jahrgang, Nr. 6093, 2012, S. 473–476, doi:10.1126/science.1222505 (sciencemag.org).
  17. ↑ Suzanne J. Admiraal & Daniel Herschlag: Mapping the transition state for ATP hydrolysis: implications for enzymatic catalysis. In: Chemistry & Biology. 2. Jahrgang, Nr. 11, 1995, S. 729–739, doi:10.1016/1074-5521(95)90101-9 (sciencedirect.com).
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  20. ↑ Herrick Baltscheffsky , Bengt Persson: On an Early Gene for Membrane-Integral Inorganic Pyrophosphatase in the Genome of an Apparently Pre-LUCA Extremophile, the Archaeon Candidatus Korarchaeum cryptofilum. In: Journal of Molecular Evolution. 78. Jahrgang, Nr. 2, 2014, S. 140–147, doi:10.1007/s00239-014-9610-7.
  21. ↑ Suzanne J. Admiraal & Daniel Herschlag: Mapping the transition state for ATP hydrolysis: implications for enzymatic catalysis. In: Chemistry & Biology. 2. Jahrgang, Nr. 11, 1995, S. 729–739, doi:10.1016/1074-5521(95)90101-9 (sciencedirect.com).
  22. ↑ Wolfgang Nitschke, Shawn E. McGlynn, E. James Milner-White, Michael J. Russell: On the antiquity of metalloenzymes and their substrates in bioenergetics. In: Geochimica et Cosmochimica Acta. 1827. Jahrgang, 8-9 Metals in Bioenergetics and Biomimetics Systems, 2013, S. 871–881, doi:10.1016/j.bbabio.2013.02.008 (sciencedirect.com).
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  24. ↑ Herrick Baltscheffsky: Origin and evolution of biological energy conversion. Hrsg.: Herrick Baltschefsky und so. John Wiley & Sons,, 1996, Energy conversion leading to the origin and early evolution of life: did inorganic pyrophosphate precede adenosine triphosphate?.
  25. ↑ Heidi H. Luoto, Georgiy A. Belogurov, Alexander A. Baykov, Reijo Lahti, and Anssi M. Malinen: Na+-translocating Membrane Pyrophosphatases Are Widespread in the Microbial World and Evolutionarily Precede H+-translocating Pyrophosphatases. In: J. Biol. Chem. 286. Jahrgang, Nr. 11, 2011, S. 21633–21642, doi:10.1074/jbc.M111.244483.
  26. ↑ Armen Y Mulkidjanian, Kira S Makarova, Michael Y Galperin, Eugene V Koonin: Inventing the dynamo machine: the evolution of the F-type and V-type ATPases. In: Nature Reviews Microbiology. 5. Jahrgang, Nr. 11, 2007, S. 892–899, doi:10.1038/nrmicro1767 (nature.com [PDF]).
  27. ↑ Armen Y Mulkidjanian, Michael Y Galperin, Kira S Makarova, Yuri I Wolf and Eugene V Koonin: Evolutionary primacy of sodium bioenergetics. In: Biology Direct. 3. Jahrgang, Nr. 13, 2008, doi:10.1186/1745-6150-3-13 (biomedcentral.com).
  28. ↑ Armen Y. Mulkidjanian, Pavel Dibrov, Michael Y. Galperin: The past and present of sodium energetics: May the sodium-motive force be with you. In: Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1777. Jahrgang, Nr. 7-8, 2008, S. 985–992, doi:10.1016/j.bbabio.2008.04.028 (sciencedirect.com).
  29. ↑ Masayoshi Maeshima: Vacuolar H+-pyrophosphatase. In: Biochimica et Biophysica Acta (BBA) - Biomembranes. 1465. Jahrgang, Nr. 1. - 2., 2000, S. 37–51, doi:10.1016/S0005-2736(00)00130-9 (els-cdn.com [PDF]).
  30. ↑ Georg Fuchs and Hans Günter Schlegel and Thomas Eitinger: Allgemeine Mikrobiologie. 9., vollständig überarbeitete und erweiterte Auflage. Georg Thieme Verlag, Stuttgart 2014, ISBN 978-3-13-44609-8(?!), Kap. 15, S. 472 links unten.
  31. ↑ Yoko Chiba, Ryoma Kamikawa, Kumiko Nakada-Tsukui, Yumikoco Saito-Nakano & Tomoyoshi Nozaki: Discovery of PPi-type Phosphoenolpyruvate Carboxykinase Genes in Eukaryotes and Bacteria. In: Journal of Biological Chemistry. 290. Jahrgang, Nr. 39, 2015, S. 23960–23970, doi:10.1074/jbc.M115.672907 (jbc.org).
  32. ↑ Marco Zancani, Valentino Casolo, Carlo Peresson, Giorgio Federici, Andrea Urbani, Francesco Macrı̀, Angelo Vianello: The β-subunit of pea stem mitochondrial ATP synthase exhibits PPiase activity. In: Mitochondrion. 3. Jahrgang, Nr. 2, 2003, S. 111–118, doi:10.1016/S1567-7249(03)00105-3 (els-cdn.com [PDF]).
  33. ↑ M. Stitt: Pyrophosphate as an alternative energy donor in the cytosol of plant cells: an enigmatic alternative to ATP. In: Bot. Acta. 111. Jahrgang, 1998, S. 167–175.
  34. ↑ Charles-David Dubé, Serge R. Guiot: Advances in Biochemical Engineering/Biotechnology (09/2015) Biogas Science and Technology. Hrsg.: M. Georg Guebitz, Alexander Bauer, Guenther Bochmann, Andreas Gronauer, Stefan Weiss. Springer International Publishing, Cham 2015, ISBN 978-3-319-21993-6, Direct Interspecies Electron Transfer in Anaerobic Digestion: A Review, S. 101–115, doi:10.1007/978-3-319-21993-6_4.
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