Incorporation of Inorganic Phosphate into Phospholipids by the Homogenate and by Sub‐Cellular Fractions of Rat Liver

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Abstract
Optimal incorporation of [32P]phosphate into phospholipids by rat liver homogenates requires the presence of NADH, Fru‐1,6‐P2 and of CMP. In the absence of 5 mM NADH and of 10 mM Fru‐1,6‐P2 little incorporation occurs. Using the experimental conditions for optimal incorporation into the phospholipids by the rat liver homogenate, attempts to incorporate [32P]phosphate into the major phospholipids of mitochondria and of microsomes were undertaken. Incorporation into either microsomes or mitochondria alone was negligible. The addition of the cytosol (supernatant) to microsomes stimulated the incorporation but had little effect on the incorporation into mitochondria. Maximal incorporation of [32P]phosphate into the major phospholipids occurred only when mitochondria, microsomes and cytosol were present together in the reaction medium. It is considered on the basis of these findings that the incorporation of the bases choline and serine into mitochondrial phospholipids observed in previous studies reflect exchange reactions and not de novo synthesis of the phospholipids by the mitochondria.