CDP-diacylglycerol tbr polyglycemphosphatid¢ biogenesis can be synthesized within rat liver mitochondria, This membrane-associated enzym¢ was predominantly lo,zated in the inner mitochondrial membrane. GTP had a significant effect in activating the microson~al CDP.diacylglycerol synthase, especially if the microsomes were preineubated with GTP in the presence of phosphatidic acid. This stlmulatory effect of GTP on the microsomal enzyme was not detected in the mitochondrial fractions, The enzymes could be solubilized from the membrane fractions usina CHAPS, and the detergent-soluble activity partially restored by addition of phospholipids. Mitechondrial and microsomal CDP-diacylglye.erol synthase activity could be completely separated by anion-exchange column ehromatograph.v. The mitoehondrlal and microsomal CDP.dlacylglycerol synthases appear to be two distinct enzymes with different localization and regulatory characteristics.

CDP-diacylglycerol for polyglycerophosphatide biogenesis can be synthesized within rat liver mitochondria. Contamination by microsomal membranes cannot account for the CDP-diacylglycerol synthesis found in the mitochondria. Phosphatidic acid from egg lecithin was the best substrate for the synthesis of CDP-diacylglycerol in both subcellular fractions. Concentration curves for CTP and Mg2+ differed for the two subcellular fractions. Microsomal CDP-diacylglycerol synthase was specifically stimulated by the nucleotide GTP; this stimulatory effect by GTP was not observed in the mitochondrial fraction. By comparison, the microsomal enzyme was more sensitive towards sulfhydryl inhibitors than the mitochondrial enzyme. The enzymes could be solubilized from the membrane fractions using 3-[(cholamidopropyl)dimethylammonio]-1-propanesulfonate, and the detergent-soluble activity could be partially restored by addition of phospholipids. Based on the differences in properties, it was concluded that there are two distinct enzyme localizations for CDP-diacylglycerol synthesis in mitochondria and microsomes from rat liver.

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