[Effect of inorganic pyrophosphate and its diphosphonate analogs on glucose-6-phosphatase dehydrogenase activity of...

The glucose-6-phosphatase dehydrogenase (EC 1.1.1.49) reaction of mouse organs was studied as affected by PPi and its diphosphonate analogs. It is shown that in vitro and hydroxy-1-ethane-1,1-diphosphonic acid) inhibit the mentioned enzyme of the mouse spleen and liver. The effect of hydroxyl-1-ethane-1,1-diphosphonic acid was used as an example to show that inhibition of glucose-6-phosphate dehydrogeanse by diphosphonates belongs to the mixed type characterized by changes in the Km and Vmax values. For the spleen enzyme Km equals 0.064 mM, Vmax - 4.7 Mg of NADPH per 1 mg of protein-1. h-1. Administration of methylene diphosphonic acid causes an inhibition in vivo of the glucose-6-phosphatase dehydrogenate activity of the liver but not of the spleen and thymus. Basing on the isoenzymic composition of the enzyme for the mentioned organs, it is possible to suppose that the difference in the methylene diphosphonic acid effect in the liver and lymphoid organs may depend on the differences in its isoenzymic spectrum. The fact that in vivo methylene diphosphonic acid in a dose having an immuno-depressive action has no influence on the activity of glucose-6-phosphatase dehydrogenase in the lymphoid organs, may evidence for the absence of the indirect immunodepressive effect of diphosphonate by affecting this enzyme.