The mechanism of substrate inhibition of palmityl coenzyme A:carnitine palmityltransferase by palmityl coenzyme A.

The substrate inhibition of palmityl coenzyme A:carnitine 0-palmityltransferase (EC 2.3.1.-) by palmityl-CoA has been studied. Beside being a substrate for the enzyme, palmityl-CoA was found to behave as a competitive inhibitor for the second substrate (carnitine). The Ki was found to be approximately 3 X 10-e M, while the K, for palmityl-CoA was found to be approximately 10M5 M. Thus, the affinity of palmityl-CoA as an inhibitor for the enzyme was at least as high as its affinity as substrate. These results explain the pronounced substrate inhibition by palmityl-CoA. The K, values for the other substrates were found to be: Lcarnitine, 2.5 X lOA M; L-palmitylcarnitine, 4 X low5 M; and CoA, 5 X 10w5M. The possible physiological importance of the reaction kinetics of carnitine pahnityltransferase is discussed.