Interaction of analogues of coenzyme A with choline acetyltransferase

The finding that methyl methanethiolsulfonate appears to inhibit choline acetyltransferase from squid ganglia not by reacting with a thiol group of the enzyme but by reacting with the thiol group of coenzyme A to form a competitive inhibitor of acetyl coenzyme A led to the synthesis of the ethyl, propyl, and 3-carboxy-4-nitrophenyl disulfides of CoA. The methyl disulfide of 1,N6-etheno-C0A, a fluorescent ligand, was also prepared. All the disulfides are powerful inhibitors of ChA, their Ki values being very similar. The Km values for acetylpropionyl-, and butyryl-CoA were also found to be similar; however, modification of the acyl group alter the Km values for choline. CoA, and dethia-CoA, showed similar abilities to be bound to ChA; however, the 3'-phospho groups of acetyl CoA and CoA appear to be of importance in interacting with the enzyme. 8-Anilino-1-naphthalenesulfonate is a competitive inhibitor of acetyl-CoA binding.