Phosphoroclastic reaction

Fe—4 S] have redox potentials sufficiently low to be active in the phosphoroclastic reaction. This would implicate that the [3 Fe—xS] centers of Fdll can be interconverted into [4 Fe-4 S]. This interconversion is supported by the fact that Fdll is only active in the last system after a lag time phase and that [4 Fe—4 S] are obtained when reconstituting Fdll. 

The fact that the same amino acid polypeptide chain can accomodate these two types of cores raises several questions what is the process that regulates the building up of a three or four iron core Is there interconversion between the two structures (as suggested by reconstitution experiments and participation of Fdll in the phosphoroclastic reaction) Is there a specific biological role for each type of structure ... 

Reduced ferredoxin reacts with proteins that participate in the dissimilatory reduction of sulfate to sulfide oxidized ferredoxin reacts with pyruvate dehydrogenase that catalyzes the conversion of pyruvate to acetyl CoA (phosphoroclastic reaction). In sulfate reduction, molecular hydrogen is the electron source, and in the phosphoroclastic reaction, protons are the terminal electron acceptor and hydrogenase mediates electron transfer between cytochrome c3 and protons or molecular hydrogen. 

This has been called the phosphoroclastic reaction. CoA and DPN are not involved in this reaction, and do not influence the rate. ... 

When grown in alkaline media, certain species of lactic acid bacteria decrease production of LDH, resulting in increased formation of formate, acetate, and ethanol as end products. This phenomenon has been observed in S. faecalis subsp. liquefaciens (Gunsalus and Niven 1942), Streptococcus durans, S. thermophilus, (Platt and Foster 1958), and Lactobacillus bulgaricus (Rhee and Pack 1980). Data of Rhee and Pack (1980) indicate that a phosphoroclastic split of pyruvate occurs under alkaline conditions to yield ATP. The enzymes involved in this reaction (pyruvate formate-lyase and acetate kinase) require alkaline conditions for optimum activity. A shift from homo- to heterofermentation because of increased pH has not been observed for Group N streptococci. 

Pyruvate formate-lyase (EC 2.3.1.54 formate acetyltransferase PEL) catalyzes the key reaction in anaerobic glucose metabolism in bacteria, the coenzyme A-dependent dismutation of pyruvate into acetyl-CoA and formate. The reaction, first reported by Werkman and co-workers in the early 1940s (169, 170), was described as the phosphoroclastic cleavage of pyruvate because acetyl phosphate was detected as a product. Following the discovery of CoA and the elucidation of its role in acetyl transfer reactions (77/, 772), the intermediacy of acetyl-CoA in pyruvate dismutation was realized the overall reaction catalyzed by PFL is generally described by two half-reactions (Scheme 37). 

Acetylphosphate CH3 COOPO(OH)2, a high energy acyl phosphate. It is the product of acetate activation in some organisms Acetate <- ATP A. p. -I- ADP, a reaction catalysed by acetate kinase (EC 2.7.2.1). The back reaction is sometimes exploited for ATP synthesis, e.g. in the phosphoroclastic fission of pyruvate. 

Bacteria can make formate in many ways. A preliminary note by Chin et al. (1957) reports that the phosphoroclastic splitting of pyruvate to HCOOH -h CH3COOH by Escherichia coli was stimulated by FH4. Huen-nekens et al. (1958) refer to similar unpublished results (Whitely, 1958) with Micrococcus aerogenes and M, lactilyticus-, serine was not an intermediate. If the reaction HCOOH H2 + CO2, also carried out by E. coli, turns out to be folic-catalyzed, the presumption would be greatly strengthened that all formate-C02 reactions require FA, as might perhaps also formate-oxalate reactions. 

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