Phosphorylation of acyclovir diphosphate by cellular enzymes

Area of Science:

• Biochemistry
• Virology
• Pharmacology

Background:

• Acyclovir is an antiviral drug, and acyclovir diphosphate (acyclo-GDP) is its active metabolite.
• Understanding the enzymes involved in acyclo-GDP phosphorylation is crucial for antiviral drug efficacy.

Purpose of the Study:

• To identify and characterize enzymes that phosphorylate acyclo-GDP.
• To determine the relative contribution of these enzymes to acyclo-GDP phosphorylation in vivo.

Main Methods:

• Enzyme kinetics studies were performed using partially purified enzymes.
• Enzyme levels and substrate/inhibitor concentrations were measured in Vero cells.
• In vivo phosphorylation rates were estimated based on kinetic data and cellular conditions.

Main Results:

• Seven enzymes, including nucleoside diphosphate kinase and pyruvate kinase, were found to phosphorylate acyclo-GDP.
• Acyclo-GDP generally exhibited lower Vmax and higher Km compared to GDP or dGDP.
• Phosphoglycerate kinase showed the highest estimated rate of acyclo-GDP phosphorylation in Vero cells, followed by pyruvate kinase and phosphoenolpyruvate carboxykinase.

Conclusions:

• The identified enzymes possess the capacity to phosphorylate acyclo-GDP.
• Phosphoglycerate kinase plays a significant role in the in vivo phosphorylation of acyclo-GDP in Vero cells.
• The combined enzymatic potential is sufficient to account for acyclo-GTP formation in cell culture.