Enzymatic Synthesis of Glycerol 1-Phosphate (D-α-Glycerophosphate)

Microsomal particulate fractions of rat organ homogenates are capable of catalyzing the synthesis of glycerol 1-phosphate1 from inorganic pyrophosphate and glycerol. The product has been isolated and characterized by elementary analysis, specific rotation, and chemical and enzymatic studies. PPi-glycerol phosphotransferase is presumably specific for the primary carbinol group of glycerol opposite to that which is phosphorylated by ATP-glycerol phosphotransferase (glycerol kinase). The distribution and some of the kinetic properties of PPi-glycerol phosphotransferase have been studied and compared with those of PPi-glucose phosphotransferase, which catalyzes the synthesis of glucose 6-phosphate. The two activities are roughly parallel in liver, kidney, and intestinal mucosa, and glucose is a competitive inhibitor of the synthesis of glycerol 1-phosphate by these organ preparations. Spleen, brain, and lung preparations catalyze the phosphorylation of glycerol from PPi while they are completely incapable of glucose 6-phosphate synthesis. In these organs glucose does not inhibit the synthesis of glycerol 1-phosphate. This suggests that there are at least two transferase enzymes which phosphorylate glycerol, one of which may be the same as the liver PPi-glucose phosphotransferase that is probably identical with glucose 6-phosphatase. Liver PPi-glycerol phosphotransferase has a pH optimum of about 5.0, is activated by preliminary treatment with deoxycholate or by NH4OH at pH 9.5, has no requirement for Mg++ or other added cofactor, and has a Km for PPi of 5 x 10-3 and for glycerol of about 3 m. The rate of hydrolysis of inorganic pyrophosphate, which proceeds simultaneously with synthetic transferase activity, is inhibited by glucose and accelerated by glycerol. This phenonemon is observed also when studied as a function of pH or of PPi, glucose, or glycerol concentration. Cytidine triphosphate or glucose-6-P can replace PPi as an efficient donor, while ATP is relatively inactive in the synthesis of glycerol 1-phosphate by the liver microsomal enzyme. Glycerol 1-phosphate is hydrolyzed at a much faster rate than is glycerol 3-phosphate by the liver microsomal preparations. This enzymatic synthesis provides a convenient method for the preparation of glycerol 1-phosphate (D-α-glycerophosphate).