Phosphorylation of acyclovir diphosphate by cellular enzymes

Abstract

Acyclovir diphosphate (acyclo-GDP) is a metabolite of the antiviral drug acyclovir [9-(2-hydroxyethoxymethyl)guanine]. Seven enzymes capable of catalyzing the phosphorylation of GDP and dGDP (nucleoside diphosphate kinase, pyruvate kinase, creatine kinase, phosphoglycerate kinase, succinyl-CoA synthetase, phosphoenolpyruvate carboxykinase and adenylosuccinate synthetase) also catalyzed the phosphorylation of acyclo-GDP. In general, acyclo-GDP had a lower V'max and a higher K'm than either GDP or dGDP. None of these enzymes showed significantly higher rates of phosphorylation with GDP or acyclo-GDP in herpes simplex virus-infected Vero cells as compared to uninfected Vero cells. The contribution of each enzyme to the phosphorylation of acyclo-GDP in vivo was estimated from the kinetic data from the partially purified enzymes, the level of each enzyme in Vero cells, and the physiological concentrations of both substrates and inhibitors. The relative order of estimated rates of acyclo-GDP phosphorylation in Vero cells was phosphoglycerate kinase much greater than pyruvate kinase greater than phosphoenolpyruvate carboxykinase greater than nucleoside diphosphate kinase greater than succinyl-CoA synthetase greater than creatine kinase greater than adenylosuccinate synthetase. The calculated potential for acyclo-GDP phosphorylation by these enzymes was adequate to account for the amounts of acyclo-GTP formed in cell culture.