Biosynthesis of acyl dihydroxyacetone phosphate in subcellular fractions of rat liver.

The activity of acyl-CoA: dihydroxyacetone phosphate acyltransferase in rat liver was studied by measuring the formation of labeled lipid from dihydroxyacetone [W]phosphate and either palmitoyl-CoA or a mixture of palmitate, CoA, and ATP. Bovine serum albumin stimulated the activity of the enzyme several-fold. In the presence of albumin the acyltransferase activity in mitochondria was much higher than in microsomes. The labeled lipid was identified as acyl dihydroxyacetone phosphate by its chromatographic and chemical properties. The acyl dihydroxyacetone phosphate-synthesizing enzyme was also present in particulate fractions of rat kidney, heart, testis, spleen, brain, and adipose tissue. The formation of glycerolipid from dihydroxyacetone phosphate in rat liver mitochondria and microsomes was also studied by using [1-W]palmitate, ATP, CoA, and other cofactors. [W]Acyl dehydroxyacetone phosphate was the principal product in both mitochondria and microsomes. Phosphatidic acid and neutral glycerides were formed when either NADPH or NADH was also included in the reaction mixture. However, the major amount of glycerides formed in the presence of NADH was, possibly, due to the acylation of glycerol 3-phosphate. The glycerol 3-phosphate was formed in the reaction mixture by the reduction of the added dihydroxyacetone phosphate with NADH, catalyzed by the glycerophosphate dehydrogenase (EC 1.1.1.8) present in the mitochondrial or microsomal fractions. This activity of the glycerophosphate dehydrogenase could not be removed from mitochondrial or microsomal particles by repeated washings with 0.25 M sucrose.