Inhibition by adenosine triphosphate of heart microsomal neutral lipase activity

Triacylglycerol lipolysis was inhibited by palmitate, in the isolated perfused normal rat heart. Acetate or acetylcarnitine could reproduce the inhibitory effects of palmitate. Since heart neutral lipase plays an important role in the lipolysis of heart triacylglycerols, the effects of acetylcarnitine, acetyl CoA and related metabolites on the microsomal neutral lipase activity were studied. ATP inhibited the enzyme activity in a concentration-dependent manner without a lag phase. AMP and adenylyl imidodiphosphate, two compounds structurally related to ATP but whose phosphate groups cannot be transferred, did not inhibit the microsomal lipase activity. These results suggested that ATP inhibited the lipase activity through the transfer of its phosphate group. It is proposed that cellular ATP concentration is a determinant of tricylglycerol lipolysis in the heart.