Malonyl-CoA decarboxylase from the uropygial gland of goose was inactivated by treatment with low concentrations of acetic anhydride in Tris-acetate buffer. 2. The degree of inactivation depended on the concentration of the reagent and time of incubation. 3. Treatment of the enzyme with [1-14C] acetic anhydride resulted in covalent attachment of the label exclusively to the decarboxylase protomer. 4. Evidence is presented that the label incorporated into the protein was exclusively in N-epsilon-acetyllysine. Graphical analysis suggested that acetylation of about two lysine residues/subunit would be required for complete inactivation of the enzyme. 5. Malonyl-CoA, acetyl-CoA, propionyl-CoA and methylmalonyl-CoA afforded partial protection to the enzyme against inactivation by acetic anhydride. 6. 3'-Dephosphomalonyl-CoA was found to be an alternate substrate for the enzyme with approximately the same Km and V values as for malonyl-CoA. 7. This alternate substrate also partially protected the enzyme from inactivation, whereas adenine nucleotides with 2'-, 3', or 5'-phosphates did not protect the enzyme. 8. These results suggest that a lysine residue acetylated by acetic anhydride is essential for the enzyme activity and that it is probably at or near the active site. The results are consistent with the suggestion that the enzyme is composed of four identical subunits.
