Biosynthesis of triacylglycerols containing short-chain fatty acids in lactating cow mammary gland. Activity of diacylglycerol acyltransferase towards short-chain acyl-CoA esters.

1. Microsomal 1,2-diacylglycerol acyltransferase from lactating cow mammary gland incorporated equal molar amounts of microsomal-bound 1,2-dipalmitoyl [2-3H]glycerol and [1-14C]-butyrate, [1-14C]hexanoate or [1-14C]palmitate from their CoA esters into triacylglycerol. The enzyme could also utilize exogenous 1,2-diacylglycerols in the presence of ethanol. 2. The pH optimum of the enzyme was 6.1 and 6.4 with butyryl-CoA and hexanoyl-CoA respectively. Values of V were approximately the same (2.7 and 2.4 nmol-min-1-mg-1, respectively), but values of Km were different (34 and 10 muM, respectively) with these two substrates. Mg2+ was not required as cofactor. 3. The presence ofa Mg2+-dependent phosphatidate phosphatase in the microsomal fraction was demonstrated. 4. It is proposed that triacylglycerols containing butyric and hexanoic acid are biosynthesized in cow mammary gland by the glycerolphosphate pathway, in which long-chain 1,2-diacylglycerols derived from phosphatidic acid are acylated at the sn-3 position by short-chain acyl-CoA esters.