ALPHA-DEUTERIUM AND BETA-DEUTERIUM KINETIC ISOTOPE EFFECTS ON THE INACTIVATION OF THE GENERAL ACYL-COENZYME-A DEHYDROGENASE FROM PIG-KIDNEY BY (2-METHYLENECYCLOPROPANE)ACETYL-COA

Seven deuterium-labeled and unlabeled forms of (2-methylenecyclopropane)acetyl-CoA (MCPA-CoA) have been employed in kinetic studies to assess alpha- and beta-deuterium isotope effects on the inactivation of the general acyl-CoA dehydrogenase from pig kidney. The racemic forms of alpha-d2-MCPA-CoA and beta-d-MCPA-CoA do not show any significant kinetic isotope effects. When inactivations of the enzyme caused by (R)-MCPA-CoA and by (R)-beta-d-MCPA-CoA or those involving (S)-MCPA-CoA and (S)-beta-d-MCPA-CoA are compared, only slight secondary deuterium isotope effects on the time versus extent of inactivation profiles are detected. These observations mitigate against one proposed mechanism for the inactivation which postulates dehydrogenation of the thioester substrate to form (2-methylenecyclopropylidene)acetyl-CoA, a reactive electrophilic Michael acceptor.