GMP reductase EC 1.7.1.7 is an enzyme that catalyzes the irreversible and NADPH-dependent reductive deamination of GMP into IMP.NADPH + guanosine 5-phosphate = NADP+ + inosine 5-phosphate + NH3By converting guanosine nucleotides to inosine nucleotides, which serve as precursors to both adenosine and G nucleotides, it helps maintains intracellular balance of A and G nucleotides. Wikipedia