The biosynthesis of short-chain triacylglycerols by microsomal fractions from lactating-cow mammary gland.

latter were present, the amount of label in the glycerol moiety of the triacylglycerols was increased &fold and that in the diacylglycerol fraction was increased 3-fold. Fatty acids derived from glucose were found mainly in the triacylglycerols, especially in the presence of exogenous free fatty acids, although appreciable amounts of label again accumulated in the diacylglycerols. The finding that fatty acids, formed de nouo from acetate or glucose, could accumulate in the diacylglycerols in rat adipose tissue appeared to be at variance with the observation that the hydrolysis of phosphatidic acid to diacylglycerol by phosphatidate phosphohydrolase is the rate-limiting step in triacylglycerol biosynthesis in rat adipose tissue (Christie et al., 1976). Fatty acid synthesis de nouo may also have a controlling function.