The Effects of Detergents on Palmityl Coenzyme A:Carnitine Palmityltransferase

The effect of detergents on the activity of palmityl coenzyme A:carnitine O-palmityltransferase (EC 2.3.1.-) has been investigated. A series of detergents (d-palmitylcarnitine, palmitylcholine, caprinylcholine, free fatty acids, deoxycholate, digitonin, Tween 20, Tween 80, and Triton X-100) have been found to stimulate the incorporation of l-carnitine-CH3-3H into l-palmitylcarnitine in the presence of CoA. The effects of d-palmitylcarnitine and Tween 80 were investigated further by studying their effects on the reaction Palmityl-CoA + carnitine ⇆ palmitylcarnitine + CoA in both directions. The effects of these detergents were found to depend on the concentration of palmityl-CoA in the reaction mixture. With high concentrations of palmityl-CoA, the detergents stimulated the transfer of palmityl groups from palmityl-CoA to carnitine. Concomitantly, the apparent Km for carnitine decreased. With low concentrations of palmityl-CoA, the detergents were inhibitory to palmityl transfer. In this case no significant change in the Km for carnitine was observed. The detergents initially had no or only a weak inhibitory effect on the palmityl transfer from palmitylcarnitine to CoA, but, as the reaction proceeded, their effect changed to stimulation because they prevented a strong product inhibition by palmityl-CoA. The mechanism of the detergent action is discussed, and it is concluded that their main effect is to prevent palmityl-CoA from acting as a competitive inhibitor of l-carnitine (and l-palmitylcarnitine). The substrate function of palmityl-CoA is also interfered with, but to a relatively much smaller extent than its inhibitory function.