Pyruvate formation

The growth of Bacillus subtilis may take place under a variety of conditions (a) aerobic conditions, (b) using nitrate as electron acceptor, and (c) fermentative conditions with glucose provided pyruvate is available as an electron acceptor since the organism lacks pyruvate formate hydrogen lyase (Nakano and Zuber 1998). 

Wagner AFV, M Frey, FA Neugebauer, W Schafer (1992) The free radical in pyruvate formate-lyase is located on glycine-734. Proc Natl Acad USA 89 996-1000. 

Knappe, J. and Sawers, G. (1990) A radical-chemical route to acetyl-CoA the anaerobically induced pyruvate formate-lyase system of Escherichia coli. FEMS Microbiology Reviews 75, 383-398. 

Methylene blue and other reducible dyes were shown to enhance the activity of NADPHa-linked MHbR (K8, K9). This is confirmed by the finding that intravenous injections of methylene blue in methemo-globinemic patients result in a striking decrease of MHb levels (e.g., B14, K9, K10). This seems to be paradoxical, since methylene blue is capable of reacting with Hb with formation of MHb, but the dye reacts much more effectively as an artificial electron carrier in the NADPH2-MHbR Systran (B14). It has been stated (K10) that methemoglobin reduction is associated with the formation of pyruvate in equivalent amounts, but that in reactions accelerated by reducible dyes no correlation between pyruvate formation and MHb reduction could be found. 

The realization of the widespread occurrence of amino acid radicals in enzyme catalysis is recent and has been documented in several reviews (52-61). Among the catalytically essential redox-active amino acids glycyl [e.g., anaerobic class III ribonucleotide reductase (62) and pyruvate formate lyase (63-65)], tryptophanyl [e.g., cytochrome peroxidase (66-68)], cysteinyl [class I and II ribonucleotide reductase (60)], tyrosyl [e.g., class I ribonucleotide reductase (69-71), photosystem II (72, 73), prostaglandin H synthase (74-78)], and modified tyrosyl [e.g., cytochrome c oxidase (79, 80), galactose oxidase (81), glyoxal oxidase (82)] are the most prevalent. The redox potentials of these protein residues are well within the realm of those achievable by biological oxidants. These redox enzymes have emerged as a distinct class of proteins of considerable interest and research activity. 

Studies on three different iron-sulfur enzyme systems, which all require S-adenosyl methionine—lysine 2,3-aminomutase, pyruvate formate lyase and anaerobic ribonucleotide reductase—have led to the identification of SAM as a major source of free radicals in living cells. As in the dehydratases, these systems have a [4Fe-4S] centre chelated by only three cysteines with one accessible coordination site. The cluster is active only in the reduced... 

Pyruvateiferredoxin 2-oxidoreductase, PYRUVATE SYNTHASE PYRUVATE FORMATE LYASE PYRUVATE KINASE... 

Figure 6-1. The steps of glycolysis. Feedback inhibition of glucose phosphorylation by hexokinase, inhibition of pyruvate kinase, and the main regulatory, rate-limiting step catalyzed by phosphofructoki-nase (PFK-I) are indicated, pyruvate formation and substrate-level phosphorylation are the main outcomes of these reactions. Regeneration of NAD occurs by reduction of pyruvate to lactate during anaerobic glycolysis.

The enzymes that utilise Fe-S clusters and S-adenosylmethionine to generate radicals essential for catalysis are now identified as a class or superfamily, the radical-SAM enzymes. Hoffman et al. have studied the pyruvate formate-lyase activating enzyme (PFL-AE) by cw EPR (X-band) and pulsed ENDOR (2H and 13C, Q-band) and used the S = signals of the Fe4S4 cluster and derivatives to construct a model for the interaction of adenosylmethionine with the cluster.86... 

Boxma B, Voncken F, Jannink S, van Alen T, Akhmanova A, van Weelden SWH, van Hellemond JJ, Ricard G, Huynen M, Tielens AGM, Hackstein JHP (2004) The anaerobic chytridiomycete fungus Piromyces spE2 produces ethanol via pyruvate formate lyase and an alcohol dehydrogenase E. Mol Microbiol 51 1389-1399 Brocks JJ, Love GD, Summons RE, Knoll AH, Logan GA, Bowden SA (2005) Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea. Nature 437 866-870... 

Fig. 5 Speculative metabolic schemes of the main pathways in carbohydrate metabolism in Trimyema compressum (after Goosen et al. 1990). End products are in boxes. Abbreviations AcCoA, acetyl-Co A, Hyd, hydrogenase, PEP, phosphoenolpyruvate carboxykinase, PFL, pyruvate formate lyase, PFO, pyruvate ferredoxin oxidoreductase, PYR, pyruvate, Xox, red> unknown electron carrier...

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