Evidence that the NiFe-carbonyl complex of co-dehydrogenase is an intermediate in the pathway of anaerobic acetyl-CoA synthesis

Conference · Mon Mar 11 04:00:00 EST 1991 · FASEB Journal (Federation of American Societies for Experimental Biology); (United States)

OSTI ID:5265848

Gorst, C M; Ragsdale, S W ^[1]

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1. Univ. of Wisconsin, Milwaukee (United States)

CO-dehydrogenase (CODH) from Clostridium thermoaceticum is a key enzyme in the anaerobic fixation of CO{sub 2} via the acetyl-CoA pathway. When reacted with CO, CODH exhibits an EPR signal which arises from a metal-carbon complex consisting of Ni, 3-4 Fe, acid labile sulfide, and CO and is referred to as the NiFeC signal. The NiFeC signal also is formed from CO{sub 2} under reducing conditions and is perturbed by substrates, CoA and acetyl-CoA, suggesting that the NiFeC species is an intermediate in the acetyl-CoA pathway. Here the authors have obtained direct evidence that the NiFeC species is a catalytically competent and physiologically significant intermediate in the synthesis of acetyl-CoA and in reduction of CO{sub 2} to CO. The authors have shown that the NiFeC species can be formed by incubation of CODH with acetyl-CoA under reducing conditions. Formation of this signal occurs at a midpoint potential of {minus}540 mV vs. NHE. The authors observed an isotope exchange between the C-1 of acetyl-CoA and the NiFeC species at rates faster than the overall isotope exchange between acetyl-CoA and CO. These experiments directly implicate the NiFeC species as an intermediate in this isotope exchange reaction. The NiFeC signal can also be generated by K{sub 2}CO{sub 3} and the authors observed an exchange reaction between acetyl-CoA and K{sub 2}CO{sub 3}. CODH reduces COS, and CO{sub 2} analogue, at a rate of 2 {mu}mole/min mg with a K{sub m} for COS of {approx} 28.9 mM. They also observed inhibition of the CO oxidation activity of CODH, with an apparent K{sub i} of 424 {mu}M, by COS. Perturbation of the NiFeC signal by COS suggests that COS binds at or near the CO/CO{sub 2} binding site.

• DOE Contract Number: FG02-88ER13875
• OSTI ID: 5265848
• Report Number(s): CONF-9104107--
• Conference Information: Journal Name: FASEB Journal (Federation of American Societies for Experimental Biology); (United States) Journal Volume: 5:4
• Country of Publication: United States
• Language: English

Related Subjects

560300* -- Chemicals Metabolism & Toxicology
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ANAEROBIC CONDITIONS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL PATHWAYS
CARBON COMPOUNDS
CARBON DIOXIDE FIXATION
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COENZYMES
COMPLEXES
ELECTRON SPIN RESONANCE
ENZYME ACTIVITY
ENZYMES
KINETICS
MAGNETIC RESONANCE
MEMBRANE PROTEINS
METABOLISM
ORGANIC COMPOUNDS
OXIDES
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PROTEINS
REACTION KINETICS
RECEPTORS
RESONANCE