An examination of the relation between endogenous lipid and the activity of the phosphatidylgrycerol-forming enzyme system in beef heart mitochondria and microsomes
The effect of endogenous lipid on the biosynthesis of phosphatidylglycerol in beef heart mitochondria and microsomes has been studied by assaying the CDP-D-diglyceride-dependent conversion of L-glycero-3-phosphate-2-3H to phosphatidylglycerol. It was found that lipid-depleted (by wafer–acetone–ammonia treatment) subcellular particles retained in mitochondria 30% and in microsomes 71% of the original activity found in lipid-containing subcellular particles. Mitochondria extracted with ether for a prolonged time (20 min) lost all activity, while mitochondria treated with water–acetone (but without ammonia) still retained 61% of the phosphatidylglycerol-forming activity. The loss of activity was found to be irreparable either by the addition of extracted endogenous lipid of subcellular particles, or by the addition of chemically well-defined lipids. Some implications of the experimental findings concerning the possible role of endogenous lipid in the activity of the enzyme system catalyzing the formation of phosphatidylglycerol in subcellular particles are discussed.