Biosynthesis of phosphatidate and neutral glycerides from triose phosphates by rat liver microsomes

Abstract

It has been suggested that there are biosynthetic mechanisms for glyceride synthesis other than the L-glycerol-3-phosphate pathway. These alternate routes utilize dihydroxyacetone phosphate and glyceraldehyde-3-phosphate as direct acyl acceptors. Present investigations show that rat liver microsomes, washed by resuspension in 0.25 M sucrose and dihydroxyacetone phosphate or glyceraldehyde-3-phosphate and labeled palmitic acid. Cofactors required for this process are ATP, CoA, Mg²�and either NADH or NADPH. NADH is twice as active as NADPH. In the absence of these reduced pyridine nucleotides, fatty acid incorporation is minimal and appreciable amounts the monoacyl derivatives of dihydroxyacetone phosphate or glyceraldehyde-3-phosphate are not formed. In the presence of either reduced pyridine nucleotide, fatty acid incorporation is stimulated and phosphatide is formed. Thus, the synthesis of acyl triose phosphates depends on their utilization for phosphatidate synthesis. Small amounts of two labeled unknown lipids are observed after incubations of triose phosphates with labeled fatty acid. Upon thin layer separation, one of the unknown lipids co-chromatograph with authentic monoacyl-dihydroxyacetone while the other unknown co-chromatograph with monoacyl-glyceraldehyde. These acylated trioses may be produced from acyl-triose phosphates by the action of phosphatases. This may explain the lack of monoacyl-triose phosphates in the experiments..