Purine nucleotide cycle

Schematic showing the purine nucleotide cycle; this pathway catalyzes the conversion of two adenosine diphosphate (ADP) molecules into one molecule of adenosine triphosphate (ATP) and one molecule of adenosine monophosphate (AMP). The AMP may then be deaminated to inosine monophosphate (IMP) by myoadenylate deaminase, with concurrent production of ammonia. The enzymes involved are: 1, myodenylate deaminase (MADA); 2, adenylosuccinate synthetase; 3, adenylosuccinate lyase; 4, ATPase; 5, muscle adenylate kinase.