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The Mechanism of Action of Ethanolamine Ammonia-Lyase, a B12-dependent Enzyme

1974; Elsevier BV; Volume: 249; Issue: 6 Linguagem: Inglês

10.1016/s0021-9258(19)42844-5

1083-351X

Bernard Babior, Thomas J. Carty, Robert H. Abeles,

Cassava research and cyanide

Abstract When l-2-aminopropanol is added to a reaction mixture containing ethanolamine ammonia-lyase and adenosylcobalamin, the carbon-cobalt bond of adenosylcobalamin is rapidly cleaved. The adenosyl moiety of the cofactor accumulates as 5'-deoxyadenosine, or a compound which readily converts to 5'-deoxyadenosine, while the cobalamin moiety is converted to a species with a spectrum resembling that of cob(II)alamin. No loss in enzymatic activity occurs. The presence of 5'-deoxyadenosine, therefore, cannot be associated with inactivation of the enzyme. The formation of 5'-deoxyadenosine from adenosylcobalamin is reversible. This provides further evidence for intermediate involvement of the nucleoside in the catalytic process. Upon longer incubation with l-2-aminopropanol, the enzyme-adenosylcobalamin complex losses its activity, while its spectrum changes to that of hydroxocobalamin. Upon denaturation, 5'-deoxyadenosine is again isolated. We tentatively attribute this inactivation to the decomposition of a (hypothetical) intermediate substrate-cobalamin adduct.