The biosynthesis of glycerides by mitochondria from rat liver. The requirement for a soluble protein

Abstract

The synthesis of glycerides from L-3-glycerophos-phate and palmitic acid by mitochondrial preparations from rat liver was shown to be stimulated markedly by a soluble factor from the supernatant fraction of the liver. That the soluble factor was a protein was indicated by its inactivation after treatment with papain and after boiling for 3 min. at 100[degree], its precipitation by (NH4)2SO4 and its behavior on Sephadex G-200. The soluble factor was purified by fractionation and gel filtration. Bovine serum albumin and lipoprotein fractions from rat and human serum also stimulated glyceride biosynthesis but the stimulations were 1/20 to 1/3 of that obtained with the soluble factor. The function of the soluble factor could not be explained by assuming a leakage of acyl-CoA synthetase, phosphatidate phosphatase or diglyceride acyltransferase from the mitochondria into the supernatant during preparation of the mitochondrial fraction. Palmitic acid, in the presence of the soluble factor and optimum amounts of ATP and CoA, was a more effective substrate than palmitoyl-CoA or palmitoylcarnitine for the biosynthesis of glycerides by mitochondria.