Carnitine Palmityltransferase Activity Research Articles

Preferential loss of ATP-dependent long-chain fatty acid activating enzyme in mitochondria prepared using nagarse

Skeletal muscle mitochondria, prepared by methods using the proteinase, Nagarse, are able to oxidize fatty acylcarnitines but not long-chain free fatty acids. Evidence obtained shows that this is not due to a lack of ATP-dependent long-chain fatty acid activating enzyme but because of the marked selective susceptibility of this enzyme to the action of Nagarse. The carnitine palmityltransferase activity is relatively stable to Nagarse. Exposure of the rat liver mitochondria to Nagarse also led to a loss of the ATP-dependent long-chain fatty acid activating enzyme but not that of monoamine oxidase. These results suggest that the ATP-dependent long-chain fatty acid activating enzyme may be localized on the outer side of the outer mitochondrial membrane.

Studies on the Control of Fatty Acid Synthesis: I. STIMULATION BY (+)-PALMITYLCARNITINE OF FATTY ACID SYNTHESIS IN LIVER PREPARATIONS FROM FED AND FASTED RATS

Abstract Hepatic long chain fatty acid synthesis from labeled acetate but not labeled malonyl coenzyme A was greatly increased by dl-palmitylcarnitine or (+)-palmitylcarnitine. Only long chain fatty acyl carnitine derivatives were effective in stimulating lipogenesis. The increase induced by 50 µm (+)-palmitylcarnitine was approximately 5-fold in liver supernatant fractions prepared from fed rats and 10-fold in preparations from fasted animals. (-)-Carnitine and (-)-palmitylcarnitine also increased fatty acid synthesis from acetate, but to a considerably lesser extent. Deoxycarnitine decreased acetate incorporation into fatty acids. Rates of acetate incorporation into fatty acids by fasted liver preparations supplemented with (+)-palmitylcarnitine were higher than those obtained in nonsupplemented livers from fed rats, but were still less than values achieved in (+)-palmitylcarnitine-treated livers from fed animals. Stimulation of fatty acid synthesis by (+)-palmitylcarnitine was shown to be at the level of malonyl-CoA formation. Partially purified preparations of acetyl-CoA carboxylase were activated equally well by either (+)- or (-)-palmitylcarnitine at all citrate concentrations tested, provided that enzyme preparations were free of carnitine palmityltransferase activity. Palmityl-CoA inhibition of acetyl-CoA carboxylase was partially relieved by (+)-palmitylcarnitine in the presence or absence of citrate or malonate. It was concluded that inhibition of hepatic fatty acid synthesis observed in fasted rats could not be accounted for by a decrease in enzyme capacity. Enzymes required for lipogenesis were present but masked in livers from fasted animals. It appeared that acetyl-CoA carboxylase in the complex system was inhibited by a factor (factors) such as palmityl-CoA which could be reversed by (+)-palmitylcarnitine addition, but not by citrate or malonate. (+)-Palmitylcarnitine stimulation of fatty acid synthesis could not be accounted for by invoking inhibition of carnitine palmityltransferase. The possible role of (-)-palmitylcarnitine formation from palmityl-CoA and relationships between effects of the two fatty acyl derivatives on the control of fatty acid synthesis are discussed.