The Participation of an Enzyme-bound Oxygen Group in a Coenzyme A Transferase Reaction

A well supported mechanism for succinyl-CoA:3-ketoacid coenzyme A transferase (EC 2.8.3.5) involving an enzyme-CoA intermediate requires the participation of an oxygen atom of the enzyme or of the CoA moiety. Measurements of loss of 18O from acetoacetate show that CoA oxygens do not participate. An oxygen-containing group on the enzyme is reversibly labeled from succinate-18O in the presence of acetoacetyl-CoA or succinyl-CoA. The 18O-labeled enzyme does not contain succinyl or CoA moieties. A binding of acetoacetate-14C to the enzyme preparation does not appear to reflect an anhydride precursor to the enzyme-CoA form.