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Demonstration of carbon-carbon bond cleavage of acetyl coenzyme A by using isotopic exchange catalyzed by the CO dehydrogenase complex from acetate-grown Methanosarcina thermophila.
Authors:S A Raybuck   S E Ramer   D R Abbanat   J W Peters   W H Orme-Johnson   J G Ferry     C T Walsh
Affiliation:Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts.
Abstract:The purified nickel-containing CO dehydrogenase complex isolated from methanogenic Methanosarcina thermophila grown on acetate is able to catalyze the exchange of [1-14C] acetyl-coenzyme A (CoA) (carbonyl group) with 12CO as well as the exchange of [3'-32P]CoA with acetyl-CoA. Kinetic parameters for the carbonyl exchange have been determined: Km (acetyl-CoA) = 200 microM, Vmax = 15 min-1. CoA is a potent inhibitor of this exchange (Ki = 25 microM) and is formed under the assay conditions because of a slow but detectable acetyl-CoA hydrolase activity of the enzyme. Kinetic parameters for both exchanges are compared with those previously determined for the acetyl-CoA synthase/CO dehydrogenase from the acetogenic Clostridium thermoaceticum. Collectively, these results provide evidence for the postulated role of CO dehydrogenase as the key enzyme for acetyl-CoA degradation in acetotrophic bacteria.
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