Regulation of Adenosine Monophosphate Levels as a Function of Adenosine Triphosphate and Inorganic Phosphate

In vitro kinetic studies with adenosine monophosphate nucleosidase (AMP nucleosidase, which catalyzes the reaction: AMP MgATP2-/→ adenine + ribose 5-phosphate) and in vivo metabolic studies with intact Azotobacter vinelandii suggest that AMP nucleosidase may be involved in removing AMP from the cellular adenylate pool under conditions where the adenylate energy charge decreases. Kinetic studies with the purified enzyme show a decrease in activity with increasing physiological levels of adenylate energy charge. In addition, millimolar levels of inorganic phosphate cause marked inhibition of AMP nucleosidase over the entire range of adenylate charge with a total adenylate pool of 2 mm. When growing cultures of A. vinelandii with 14C-labeled adenylate pools were subjected to anaerobic conditions, the ATP levels decreased rapidly with a concomitant rise in AMP, followed by a rise in hypoxanthine. These observations are consistent with the increased levels of intracellular AMP being removed by AMP nucleosidase. The resultant adenine can then be converted to hypoxanthine by adenase.