Studies on nucleotide diphosphate diacylglycerol specificity of acidic phospholipid biosynthesis in rat liver subcellular fractions

Abstract

1. (1) Cytidine diphosphate diacylglycerol, uridine diphosphate diacylglycerol, adenosine diphosphate diacylglycerol and guanosine diphosphate diacylglycerol were synthesized chemically and their purity assessed. The activity of these compounds in acidic phospholipid synthesis was examined in rat liver mitochondria and microsomes. 2. (2) Phosphatidylglycerol synthesis in rat liver mitochondria exhibited considerable activity with CDPdiacylglycerol ( V 7.0 nmol · mg −1 · h −1), UDPdiacylglycerol ( V 5.4) and ADPdiacylglycerol ( V 4.2). GDPdiacylglycerol activity was detectable but very low. 3. (3) Diphosphatidylglycerol formation in mitochondria and phosphatidyl-inositol synthesis in microsomes exhibited considerable more specificity for CDPdiacylglycerol. However, at high concentrations, measurable diphosphatidylglycerol and phosphatidylinositol synthesis was observed with the other liponucleotides. 4. (4) Although considerable phosphatidylglycerol formation was observed with UDPdiacylglycerol and ADPdiacylglycerol, it is unlikely that these compounds are of physiologic importance, at least in rat liver, since CTP:phosphatidic acid cytidyltransferase in microsomes and mitochondria was shown to be specific for cytidine triphosphate. The lack of specificity of phosphatidylglycerol synthesis for CDPdiacylglycerol is currently unexplained but may be of some importance in other tissues or in other organisms.