Reaction of yeast fatty acid synthetase with iodoacetamide. 3. Malonyl-coenzyme A decarboxylase as product of the reaction of fatty acid synthetase with iodoacetamide.

Yeast fatty acid synthetase possesses very low malonyl-CoA decarboxylase activity. Treatment with iodoacetamide, while abolishing synthetase activity, induces a strong malonyl decarboxylase activity which, in turn, can be inhibited by N-ethylmaleimide. Kinetic analysis shows that the emergence of the decarboxylase activity is synchronized to the disappearance of the fatty-acid-synthesizing activity and thus, is due to carboxamidomethylation of the peripheral SH-groups of the multienzyme complex. Strong decarboxylase activity was also found after treatment of the synthetase with methylmalonyl-CoA. A hypothetical scheme is proposed which explains the origination of the decarboxylase activity as a consequence of conformational changes of the condensing enzyme component which happen when the peripheral SH-group is acylated or alkylated.