Key points are not available for this paper at this time.
Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. The catalytic proficiency of this enzyme for the reverse reaction, pyruvate synthase, is poorly understood. Conversion of acetyl-CoA to pyruvate links the Wood-Ljungdahl pathway of autotrophic CO2 fixation to the reductive tricarboxylic acid cycle, which in these autotrophic anaerobes is the stage for biosynthesis of all cellular macromolecules. The results described here demonstrate that the Clostridium thermoaceticum PFOR is a highly efficient pyruvate synthase. The Michaelis-Menten parameters for pyruvate synthesis by PFOR are: V max = 1.6 unit/mg (k cat = 3.2 s−1), KmAcetyl-CoA = 9 μm, and KmCO2 = 2 mm. The intracellular concentrations of acetyl-CoA, CoASH, and pyruvate have been measured. The predicted rate of pyruvate synthesis at physiological concentrations of substrates clearly is sufficient to support the role of PFOR as a pyruvate synthase in vivo. Measurements of itsk cat/K m values demonstrate that ferredoxin is a highly efficient electron carrier in both the oxidative and reductive reactions. On the other hand, rubredoxin is a poor substitute in the oxidative direction and is inept in donating electrons for pyruvate synthesis. Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. The catalytic proficiency of this enzyme for the reverse reaction, pyruvate synthase, is poorly understood. Conversion of acetyl-CoA to pyruvate links the Wood-Ljungdahl pathway of autotrophic CO2 fixation to the reductive tricarboxylic acid cycle, which in these autotrophic anaerobes is the stage for biosynthesis of all cellular macromolecules. The results described here demonstrate that the Clostridium thermoaceticum PFOR is a highly efficient pyruvate synthase. The Michaelis-Menten parameters for pyruvate synthesis by PFOR are: V max = 1.6 unit/mg (k cat = 3.2 s−1), KmAcetyl-CoA = 9 μm, and KmCO2 = 2 mm. The intracellular concentrations of acetyl-CoA, CoASH, and pyruvate have been measured. The predicted rate of pyruvate synthesis at physiological concentrations of substrates clearly is sufficient to support the role of PFOR as a pyruvate synthase in vivo. Measurements of itsk cat/K m values demonstrate that ferredoxin is a highly efficient electron carrier in both the oxidative and reductive reactions. On the other hand, rubredoxin is a poor substitute in the oxidative direction and is inept in donating electrons for pyruvate synthesis. pyruvate:ferredoxin oxidoreductase CO dehydrogenase 3-(N-morpholino)-propanesulfonate acetyl-CoA synthase lactate dehydrogenase 4-morpholineethanesulfonic acid high pressure liquid chromatography ferredoxin Organisms from all three kingdoms of life (Bacteria, Archaea, and Eukarya) metabolize pyruvate in biosynthetic and catabolic reactions. Mitochondria and aerobic bacteria couple the oxidative decarboxylation of pyruvate to the reduction of NAD+ by the pyruvate dehydrogenase multienzyme complex (1Patel M.S. Roche T.E. FASEB J. 1990; 4: 3224-3233Crossref PubMed Scopus (502) Google Scholar). In many anaerobic organisms, pyruvate:ferredoxin oxidoreductase (PFOR)1 catalyzes the oxidative decarboxylation of pyruvate to CO2 and acetyl-CoA (Reaction 1) (2Menon S. Ragsdale S.W. Biochemistry. 1997; 36: 8484-8494Crossref PubMed Scopus (62) Google Scholar, 3Hrdý I. Müller M. J. Mol. Evol. 1995; 41: 388-396Crossref PubMed Scopus (0) Google Scholar, 4Neuer G. Bothe H. Biochim. Biophys. Acta. 1982; 716: 358-365Crossref PubMed Scopus (39) Google Scholar, 5Yakunin A.F. Hallenbeck P.C. Biochim. Biophys. Acta. 1998; 1409: 39-49Crossref PubMed Scopus (43) Google Scholar, 6Adams M.W.W. Kletzin A. Adv. Protein Chem. 1996; 48: 101-180Crossref PubMed Google Scholar). In anaerobic acetogenic bacteria, 2 moles of CO2 generated from the decarboxylation of 2 moles of pyruvate are reduced to another mol of acetyl-CoA in an autotrophic biosynthetic scheme known as the Wood-Ljungdahl pathway (7Ragsdale S.W. Kumar M. Zhao S. Menon S. Seravalli J. Doukov T. Krautler B. Vitamin B12 and B12-Proteins. Wiley-VCH, Weinheim, Germany1998: 167-177Google Scholar, 8Ragsdale S.W. Biofactors. 1997; 9: 1-9Google Scholar, 9Ragsdale, S. W. (2000) in Biological Inorganic Chemistry: Structure and Reactivity (Valentine, J. S., Bertini, I., and Gray, H., eds), in press, University Science Books.Google Scholar). Thus, PFOR links glycolysis to the Wood-Ljungdahl pathway. The reverse reaction, carboxylation of acetyl-CoA, is an important reaction for anaerobes like methanogens and acetogens that fix CO2 by the Wood-Ljungdahl pathway (10Simpson P.G. Whitman W.B. Ferry J.G. Methanogenesis: Ecology Physiology, Biochemistry 169: 5327-5329Crossref PubMed Google Scholar, 12Lapado J. Whitman W.B. Proc. Natl. Acad. Sci. U. S. A. 1990; 87: 5598-5602Crossref PubMed Scopus (60) Google Scholar, 13Fuchs G. FEMS Microbiol. Rev. 1986; 39: 181-213Crossref Google Scholar). In this case, PFOR (pyruvate synthase) links the Wood-Ljungdahl pathway to the incomplete reductive tricarboxylic acid cycle, which generates biosynthetic intermediates.Pyruvate+CoASH→AcetylSCoA+CO2+2H++2e−REACTION 1 CO+H2O→CO2+2H++2e−REACTION 2 PFORs can be homo- (14Wahl R.C. Orme-Johnson W.H. J. Biol. Chem. 1987; 262: 10489-10496Abstract Full Text PDF PubMed Google Scholar) or heterodimeric (15Kerscher L. Oesterhelt D. Trends. Biochem. Sci. 1982; 7: 371-374Abstract Full Text PDF Scopus (117) Google Scholar) or heterotetrameric (6Adams M.W.W. Kletzin A. Adv. Protein Chem. 1996; 48: 101-180Crossref PubMed Google Scholar). It is thought that all PFORs evolved by rearrangements and fusions of four ancestral genes (16Kletzin A. Adams M.W.W. J. Bacteriol. 1996; 178: 248-257Crossref PubMed Google Scholar, 17Zhang Q. Iwasaki T. Wakagi T. Oshima T. J. Biochem. (Tokyo). 1996; 120: 587-599Crossref PubMed Scopus (80) Google Scholar). They contain 1–3 iron-sulfur clusters and thiamine pyrophosphate as prosthetic groups (15Kerscher L. Oesterhelt D. Trends. Biochem. Sci. 1982; 7: 371-374Abstract Full Text PDF Scopus (117) Google Scholar,18Bock A.K. Schonheit P. Teixeira M. FEBS Lett. 1997; 414: 209-212Crossref PubMed Scopus (16) Google Scholar, 19Menon A.L. Hendrix H. Hutchins A. Verhagen M. Adams M.W.W. Biochemistry. 1998; 37: 12838-12846Crossref PubMed Scopus (20) Google Scholar). The PFOR from Clostridium thermoaceticum is a 240-kDa homodimer, with two 4Fe-4S2+/1+ clusters and one thiamin pyrophosphate/subunit (2Menon S. Ragsdale S.W. Biochemistry. 1997; 36: 8484-8494Crossref PubMed Scopus (62) Google Scholar, 14Wahl R.C. Orme-Johnson W.H. J. Biol. Chem. 1987; 262: 10489-10496Abstract Full Text PDF PubMed Google Scholar) The two electrons generated by the oxidative decarboxylation of pyruvate are transferred to an 8-iron ferredoxin (or possibly other electron carriers, see below) that in turn can reduce a variety of cellular enzymes. This electron pair can also be transferred directly to CODH, which reduces CO2 to CO, an intermediate in the Wood-Ljungdahl pathway (20Menon S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google Scholar). The PFOR reaction has been most extensively studied in the forward (oxidative decarboxylation) direction beginning with a series of seminal studies published in 1971 (21Uyeda K. Rabinowitz J.C. J. Biol. Chem. 1971; 246: 3120-3125Abstract Full Text PDF PubMed Google Scholar, 22Uyeda K. Rabinowitz J.C. J. Biol. Chem. 1971; 246: 3111-3119Abstract Full Text PDF PubMed Google Scholar, 23Raeburn S. Rabinowitz J.C. Arch. Biochem. Biophys. 1971; 146: 9-20Crossref PubMed Scopus (32) Google Scholar, 24Raeburn S. Rabinowitz J.C. Arch. Biochem. Biophys. 1971; 146: 21-33Crossref PubMed Scopus (37) Google Scholar). Rabinowitz and co-workers (21Uyeda K. Rabinowitz J.C. J. Biol. Chem. 1971; 246: 3120-3125Abstract Full Text PDF PubMed Google Scholar, 22Uyeda K. Rabinowitz J.C. J. Biol. Chem. 1971; 246: 3111-3119Abstract Full Text PDF PubMed Google Scholar, 23Raeburn S. Rabinowitz J.C. Arch. Biochem. Biophys. 1971; 146: 9-20Crossref PubMed Scopus (32) Google Scholar, 24Raeburn S. Rabinowitz J.C. Arch. Biochem. Biophys. 1971; 146: 21-33Crossref PubMed Scopus (37) Google Scholar) isolated and characterized pyruvate:ferredoxin oxidoreductase. They also demonstrated that low potential electron donors, like reduced ferredoxin, can drive the reductive carboxylation of acetyl-CoA (24Raeburn S. Rabinowitz J.C. Arch. Biochem. Biophys. 1971; 146: 21-33Crossref PubMed Scopus (37) Google Scholar). 2At that time it was not clear whether acetyl-CoA was the substrate, so they used acetyl-phosphate in the presence of CoA and phosphotransacetylase. Subsequently, few studies of the pyruvate synthase activity have been published. Can PFOR also serve as a pyruvate synthase? A PFOR has been isolated from the methanogenic archaea, Methanosarcina barkeri (18Bock A.K. Schonheit P. Teixeira M. FEBS Lett. 1997; 414: 209-212Crossref PubMed Scopus (16) Google Scholar) and Methanobacterium thermoautotrophicum (25Tersteegen A. Linder D. Thauer R.K. Hedderich R. Eur. J. Biochem. 1997; 244: 862-868Crossref PubMed Scopus (61) Google Scholar). These enzymes must function in anabolic reactions, because methanogens cannot grow on substrates with a more complex structure than acetate. The M. barkeri enzyme was shown to catalyze the oxidative decarboxylation of pyruvate to acetyl-CoA and the reductive carboxylation of acetyl-CoA with ferredoxin as an electron carrier (26Bock A.K. Kunow J. Glasemacher J. Schonheit P. Eur. J. Biochem. 1996; 237: 35-44Crossref PubMed Scopus (37) Google Scholar). The sequences of the methanogenic enzymes are closely related to those of the PFORs fromPyrococus furiosus and Thermotoga maritima (25Tersteegen A. Linder D. Thauer R.K. Hedderich R. Eur. J. Biochem. 1997; 244: 862-868Crossref PubMed Scopus (61) Google Scholar,26Bock A.K. Kunow J. Glasemacher J. Schonheit P. Eur. J. Biochem. 1996; 237: 35-44Crossref PubMed Scopus (37) Google Scholar), which function in a catabolic direction (27Blamey J.M. Adams M.W.W. Biochim. Biophys. Acta. 1993; 1161: 19-27Crossref PubMed Scopus (142) Google Scholar). Thus, these combined studies indicate that the same enzyme (PFOR) functions physiologically in either direction. This conclusion is supported by the finding that under some conditions, methanogens can grow, albeit poorly, on pyruvate (28Rajagopal B.S. LeGall J. Curr. Microbiol. 1994; 28: 307-311Crossref Scopus (9) Google Scholar, 29Bock A.-K. Schönheit P. J. Bacteriol. 1995; 177: 2002-2007Crossref PubMed Google Scholar). Yoon et al. (37Yoon K.S. Hille R. Hemann C. Tabita F.R. J. Biol. Chem. 1999; 274: 29772-29778Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar) have also studied the pyruvate synthase reaction of the PFOR from Chloribium tepidum. The results described above support the hypothesis that PFOR and pyruvate synthase are the same enzyme. However, the reverse reaction of PFOR has been scantily studied and several examples exist of distinct enzymes catalyzing forward or reverse reactions. For example, fumarate reductase and succinate dehydrogenase preferentially catalyze opposing reactions (30Hirst J. Sucheta A. Ackrell B.A.C. Armstrong F.A. J. Am. Chem. Soc. 1996; 118: 5031-5038Crossref Scopus (105) Google Scholar, 31Hirst J. Ackrell B.A.C. Armstrong F.A. J. Am. Chem. Soc. 1997; 119: 7434-7439Crossref Scopus (40) Google Scholar) and are separately regulated and distinct gene products (32Maklashina E. Berthold D.A. Cecchini G. J. Bacteriol. 1998; 180: 5989-5996Crossref PubMed Google Scholar, 33Hirsch C.A. Rasminsky M. Davis B.D. Lin E.C.C. J. Biol. Chem. 1963; 238: 3770-3774Abstract Full Text PDF PubMed Google Scholar). In many organisms, H+ reduction and H2 oxidation are catalyzed by separate enzymes with the converse catalytic biases (34Pershad H.R. Duff J.L. Heering H.A. Duin E.C. Albracht S.P. Armstrong F.A. Biochemistry. 1999; 38: 8992-8999Crossref PubMed Scopus (216) Google Scholar, 35Butt J.N. Filipiak M. Hagen W.R. Eur. J. Biochem. 1997; 245: 116-122Crossref PubMed Scopus (73) Google Scholar). Can PFOR serve as an efficient pyruvate synthase or is it prejudiced toward oxidative decarboxylation? One test of its catalytic bias is to compare the specificity factor (V/K) for the two opposing reactions. Another test is to determine the relative rates of the opposite reactions at physiological substrate concentrations. A significant catalytic preference in one direction would suggest that PFOR and pyruvate synthase might be separate enzymes. The difficulty in studying pyruvate synthesis from acetyl-CoA and CO2 is that a sufficiently strong electron donor must be coupled to drive this energetically demanding reaction, with a reduction potential below −540 mV. In the have coupled pyruvate synthesis to CO oxidation by CO dehydrogenase (Reaction 2 and which has a low reduction potential E. Ragsdale S.W. J. Biol. Chem. 1990; Full Text PDF PubMed Google Scholar). PFOR and pyruvate synthase are the same one to the direction of pyruvate is for synthase to a high potential electron in the oxidative direction and a separate low potential donor in the reductive direction. For example, in the fumarate reductase and succinate dehydrogenase the low potential donor is a substrate for fumarate which has a preferentially to succinate (32Maklashina E. Berthold D.A. Cecchini G. J. Bacteriol. 1998; 180: 5989-5996Crossref PubMed Google Scholar). not which electron are most efficient in the PFOR and pyruvate synthase reactions. rubredoxin electrons from it was to be the physiological electron for the oxidative decarboxylation reaction, reduced ferredoxin was as the electron donor for the synthase reaction (37Yoon K.S. Hille R. Hemann C. Tabita F.R. J. Biol. Chem. 1999; 274: 29772-29778Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar). However, the parameters for the substrates and electron in direction not studied some electron carrier specificity the electron carrier specificity be in C. thermoaceticum is an for studying PFOR because the oxidative decarboxylation and reductive carboxylation reactions are for and autotrophic of this characterized and the rate for the in the C. thermoaceticum PFOR reaction (2Menon S. Ragsdale S.W. Biochemistry. 1997; 36: 8484-8494Crossref PubMed Scopus (62) Google Scholar). high concentrations of substrates (k cat the synthase reaction was predicted to be than the reverse the synthase reaction was not studied the intracellular concentrations of the substrates and products of the PFOR reaction in C. thermoaceticum have not been the relative rates of the opposing reactions at physiological concentrations of substrates are PFOR is an efficient pyruvate synthase for autotrophic acetogens an In the on several are the values of cat cat/K m for the reverse these values with a physiological function for PFOR in pyruvate a low potential electron CO oxidation sufficient to drive pyruvate synthesis. the C. thermoaceticum pyruvate synthase reaction couple to the CO oxidation is the most efficient electron donor and for the forward and reverse reactions of from was by a CO was from acetyl-CoA reduced dehydrogenase from from C. thermoaceticum was at in a on and CO2. CODH, and ferredoxin under anaerobic PFOR was as described (20Menon S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google Scholar) in anaerobic at S.W. J. Biol. Chem. Full Text PDF PubMed Google Scholar) and ferredoxin J. Bacteriol. 1982; PubMed Google Scholar) under anaerobic at in a below of concentrations by the J.M. Arch. Biochem. Biophys. PubMed Scopus Google Scholar) a activity was by the reduction of = S.W. J. Biol. Chem. Full Text PDF PubMed Google Scholar). PFOR activity was as described (2Menon S. Ragsdale S.W. Biochemistry. 1997; 36: 8484-8494Crossref PubMed Scopus (62) Google Scholar) by and activity was by CO oxidation by to reduction = Ferry J.G. J. Biol. Chem. Full Text PDF PubMed Google Scholar) in a reaction to that described for J.S. Biochem. PubMed Scopus Google Scholar). was from Clostridium S.W. J. Bacteriol. PubMed Google Scholar). synthase activity was in a coupled reaction with CO and CO dehydrogenase as the electron was coupled to oxidation by lactate dehydrogenase of 1 or 1 acetyl-CoA, CODH, ferredoxin, and The was under an of CO in a reaction 1 CODH, 1 or PFOR and concentrations of acetyl-CoA and CO2. The CO2 was by the the of the reaction and the the CO2 from CO was low to the CO2 concentrations in CODH, electron carrier or and concentrations in a coupled reaction to the under which pyruvate synthase activity is In all the was and with CO by for with CO in a oxidation = was in an The at and by max and m values by the to the for a PFOR has been shown to a (21Uyeda K. Rabinowitz J.C. J. Biol. Chem. 1971; 246: 3120-3125Abstract Full Text PDF PubMed Google Scholar). The determine the parameters of PFOR for ferredoxin, the reaction 1 1 thiamin 2 and concentrations of ferredoxin in The reaction was by 2 of PFOR to a reaction of and the reduction of was at = determine the parameters for the reaction with the reaction was by 1 of PFOR to a reaction and the reduction of rubredoxin was at = S.W. J. Bacteriol. PubMed Google Scholar). The concentrations of the same as for the reaction with ferredoxin that was determine the parameters for the reaction 1 1 thiamin 2 in The of pyruvate was from to mm. The reduction of was at The to the Michaelis-Menten to the max = m for pyruvate = cat/K m = C. thermoaceticum of in of for The and 1 in the with 2 m acid at at for the was to with 1 m the was and the concentrations of in the acetyl-CoA of a with was to the as an to determine from the than of the acetyl-CoA was the The of and acetyl-CoA by high liquid chromatography on a with a the of the by with a from to in a time used a these conditions, the for and for acetyl-CoA and The concentrations of and acetyl-CoA in the on a CoASH, acetyl-CoA The of pyruvate was by the lactate dehydrogenase H. R. 41: PubMed Scopus Google Scholar) of 1 H. in Clostridium University of Scholar) and a of for the of of H. Clostridium University of Scholar) used in of intracellular concentrations of for of of of with to the pyruvate synthase or PFOR reactions to the enzyme as synthesis from acetyl-CoA and CO2 a strong electron CO2 by the pyruvate decarboxylation reaction is the of the in acetyl-CoA synthesis by (20Menon S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google Scholar), coupled pyruvate synthesis to CO oxidation by The rate of pyruvate was by the lactate oxidation of to It was shown that the of an electron carrier the of PFOR to couple to CODH, a in the rate of CO (20Menon S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google Scholar). However, in the pyruvate synthase reaction, either ferredoxin or was to the electron from reduced to pyruvate synthase the of this coupled it was to under which pyruvate synthase is These 1 CODH, 1 ferredoxin, or 1 concentrations of PFOR at or below the reaction rate was concentrations of CO2 and acetyl-CoA used to the parameters for the pyruvate synthase reaction of the pyruvate synthase The at and by The of CO2 was at and concentrations of The parameters V max m by of the to a The parameters max 1.6 KmAcetyl-CoA = μm, and KmCO2 = The not a complex the parameters and KmAcetyl-CoA On the other hand, the a The parameters by the to a The parameters for the pyruvate synthase are in with those for the PFOR reaction, which also CO and as the electron the pyruvate synthase activity is CO2 and acetyl-CoA the activity is 1.6 which to a cat of 3.2 This is than cat for the PFOR reaction s−1), which with on (2Menon S. Ragsdale S.W. Biochemistry. 1997; 36: 8484-8494Crossref PubMed Scopus (62) Google Scholar). was by ferredoxin at concentrations of pyruvate and was in the that the reaction of pyruvate not electron to the is under these parameters for the pyruvate synthase and PFOR cat/K rate at physiological concentrations of synthase synthase to the PFOR S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google to the PFOR to the PFOR synthase to the PFOR synthase to the PFOR S. Ragsdale S.W. Biochemistry. 1996; 35: 12119-12125Crossref PubMed Scopus (43) Google rates at intracellular concentrations of rate at physiological concentrations of synthase to the PFOR in a rates at intracellular concentrations of used to determine the physiological electron for PFOR and pyruvate synthase 2 ferredoxin as the cat/K m for ferredoxin for the synthase reaction is than for the oxidative The 8-iron ferredoxin from the also was as an electron as the C. thermoaceticum ferredoxin that these are to in a with both PFOR and it was for the PFOR of C. that rubredoxin is the electron ferredoxin is the electron donor for the pyruvate synthase reaction (37Yoon K.S. Hille R. Hemann C. Tabita F.R. J. Biol. Chem. 1999; 274: 29772-29778Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar). This hypothesis is because rubredoxin has a potential it is have more below A. Chem. Rev. 1996; PubMed Scopus Google Scholar). However, the values of the specificity for rubredoxin and ferredoxin in the pyruvate synthase or PFOR reactions have been The cat/K m for rubredoxin in the oxidative decarboxylation reaction is which is than that for Thus, the for rubredoxin with pyruvate is in C. is a strong preference of PFOR for ferredoxin in the oxidative decarboxylation not couple CO oxidation to the pyruvate synthase reaction and rubredoxin is a highly electron for S.W. J. Biol. Chem. Full Text PDF PubMed Google Scholar), the is in the pyruvate synthase This is because the reduction potential for the couple of rubredoxin is more than that of the acetyl-CoA the physiological of the pyruvate synthase reaction of the acetyl-CoA, and concentrations in C. thermoaceticum The of these in the by related to the intracellular of = of the intracellular concentrations of and acetyl-CoA to be and The intracellular pyruvate is the CO2 is to be because are with CO2 intracellular of and A in C. = dehydrogenase = = in a the intracellular pyruvate is below its m the PFOR reaction would be by the of the pyruvate synthase reaction would be by the of acetyl-CoA in the The is at physiological concentrations of pyruvate and acetyl-CoA, the carboxylation of acetyl-CoA is predicted to than oxidative decarboxylation of these predicted the forward and reverse reactions in the presence of the intracellular concentrations of acetyl-CoA, and CO2 The results the with a of oxidative decarboxylation to reductive carboxylation of The oxidative decarboxylation of pyruvate by PFOR generates low potential electrons that can be coupled to important reactions in the and reduction to and PFOR also generates the Thus, this important reaction has been studied The reverse reaction, reduction of acetyl-CoA to is important for autotrophic anaerobes because it links the Wood-Ljungdahl pathway of acetyl-CoA to the incomplete reductive tricarboxylic acid for synthesis of biosynthetic reactions in acetogens are not in it is clear that the incomplete tricarboxylic acid from pyruvate by the of pyruvate or the of and and (10Simpson P.G. Whitman W.B. Ferry J.G. Methanogenesis: Ecology Physiology, Biochemistry PubMed Scopus Google Scholar). on of the substrate is in most of the is in acetate. In it that the pyruvate synthase activity of PFOR is sufficient to for its role in the of pyruvate as a biosynthetic is the physiological electron for pyruvate synthase and a potential for the acetyl-CoA couple of pyruvate is a strong it a strong to Tabita (37Yoon K.S. Hille R. Hemann C. Tabita F.R. J. Biol. Chem. 1999; 274: 29772-29778Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar) that rubredoxin is a strong electron for the PFOR from the C. that it be the physiological in this direction. The C. thermoaceticum is a highly electron donor and can reduce of rubredoxin in anaerobic have been These have been in to a role for rubredoxin in from G. S. LeGall J. C. Teixeira M. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, Verhagen Adams 1999; PubMed Scopus Google Scholar). is to be a electron from because its couple is mV. on the of rubredoxin electrons of than ferredoxin potential of to However, cat/K m for rubredoxin used rubredoxin from C. not C. thermoaceticum to couple to thermoaceticum because this is in of C. These electron can be used related not this to because the C. rubredoxin to the C. and C. thermoaceticum the M. ferredoxin is as an electron as the C. thermoaceticum in pyruvate oxidation is than that for Thus, the for ferredoxin reduction is relative to ferredoxin is a more efficient of electrons from more with rubredoxin as an electron for PFOR is that it is a poor electron donor for reactions. it to rubredoxin to couple pyruvate oxidation to or The and the CO2 have reduction that rubredoxin is to couple CO oxidation to the pyruvate synthase On the other hand, ferredoxin is an in this rubredoxin is inept as an electron donor for pyruvate the cat/K m for ferredoxin in the synthase reaction is than in the oxidative Thus, results indicate that PFOR is an efficient pyruvate synthase and that ferredoxin as the electron for pyruvate oxidation as as the electron donor for pyruvate synthesis.
Furdui et al. (Fri,) studied this question.