Abstract
Experiments were carried out to elucidate regulatory mechanism of fatty acid metabolism, especially fat mobilization and β-oxidation.
It was cleary demonstrated that conversion of lipase to esterase was observed in rat epididymal adipose tissue during starvation. A physiological significance of this conversion was discussed.
In rat liver, oxidation of palmitate, palmityl-carnitine and palmityl CoA were remarkably increased during fasting. Then, the effect of different carbohydrate metabolites on acyl-CoA synthetase and acyl-CoA dehydrogenase was examined. Acyl-CoA synthetase was activated by α-glycerophosphate and inhibited by citrate. Furthermore, α-glycerophosphate eliminates citrateinhibition of acyl-CoA synthetase. In contrast with the case of acyl-CoA synthetase, acyl-CoA dehydrogenase was inhibited by both α-glycerophosphate and citrate.
Therefore, when fatty acid metabolism is predominant as in case of starvation, α-glycerophosphate and citrate contents may be reduced and the inhibitory effect of these substances on acyl-CoA dehydrogenase may be eliminated, so that β-oxidation may be accelerated as a result. On the other hand, when carbohydrate metabolism is predominant, both α-glycerophosphate and citrate may inhibit acyl-CoA dehydrogenase activity, so that α-oxidation may be blocked as aresult, whereas citrate inhibition of acyl-CoA synthetase may be eliminated by α-glycerophosphate, with which acyl-CoA produced may be used for lipid synthesis. Experiments are continued to clarify whether such a regulatory mechanism exists in vivo.
