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Enzymatic Synthesis of Glycerol 1-Phosphate (d--Glycerophosphate)

INORGANIC PYROPHOSPHATE-GLYCEROL PHOSPHOTRANSFERASE AND INORGANIC PYROPHOSPHATE-GLUCOSE PHOSPHOTRANSFERASE COMPARED

From the ¹ From the Department of Medicine, Rutgers Medical School, New Brunswick, New Jersey 08903

"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. PP_i-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 PP_i-glycerol phosphotransferase have been studied and compared with those of PP_i-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 PP_i 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 PP_i-glucose phosphotransferase that is probably identical with glucose 6-phosphatase.

Liver PP_i-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 K_m for PP_i 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 PP_i, glucose, or glycerol concentration.

Cytidine triphosphate or glucose-6-P can replace PP_i 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--glycerophosphate).

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