<p> Guanosine monophosphate reductase (<db_xref db="EC" dbkey="1.7.1.7"/>) catalyzes the irreversible and NADPH-dependent reductive deamination of GMP into IMP.<reaction> NADPH + guanosine 5-phosphate = NADP+ + inosine 5-phosphate + NH3 </reaction> </p> <p> It converts nucleobase, nucleoside and nucleotide derivatives of G to A nucleotides, and maintains intracellular balance of A and G nucleotides. A deep split separates two families of GMP reductase. This family is found in a variety of bacterial lineages.</p>