THE EFFECT OF FASTING ON ESTERIFICATION OF PALMITATE BY RAT LIVER IN VITRO

Abstract

The ability of liver slices from rats fasted 48 hours to esterify palmitate-1-14C is about half of that of slices from fed animals. The same effect can be observed in homogenates of liver freed of nuclei, either with or without mitochondria. In both preparations, the synthesis of triglycerides is chiefly affected. The decrease in esterification by homogenate supernatants containing microsomes from fasted animals can be overcome by using increased amounts of ATP or an ATP generator and NaF in the incubation medium. The ATPase responsible for the higher ATP requirement in liver homogenates from fasted animals is Mg++-dependent. Higher concentrations of ATP inhibit esterification by mitochondrial preparations. Incorporation of both palmitate-9-10-3H and of glycerol-1-3-14C is reduced to the same extent for each compound in slices from fasting animals. Glycerol kinase and α-glycerophosphate dehydrogenase are both unaffected by 48 hours' fasting. It is concluded that the decrease in ATP from the activation of ATPase is responsible for the decreased esterification in the intact cell.