Microsomes, Microsomal Phospholipids, and Fatty Acid Synthesis

The effect of microsomes on fatty acid synthesis by the soluble fraction of rat liver cells has been studied. It was shown that the microsomes contain a heat-labile inhibitory factor, presumably ATPase, and a heat-stable stimulatory factor. The latter was localized in the membranes of the endoplasmic reticulum and could be activated by treatment with Pronase. The factor was extractable in lipid solvents and was shown to be phospholipid in nature. Synthetic phospholipids also stimulated fatty acid synthesis, while preliminary treatment of microsomes with phospholipase C removed stimulatory activity. The factor was shown to activate hepatic acetyl coenzyme A carboxylase and presumably stimulated fatty acid synthesis in the soluble fraction by this mechanism.