GMPR, also known as GMPR1, belongs to the IMPDH/GMPR family. This family of enzymes includes IMP dehydrogenase and GMP reductase. These enzymes are involved in purine metabolism and adopt a TIM barrel structure. GMPR is an enzyme that catalyzes the irreversible and NADPH-dependent reductive deamination of GMP to IMP. GMPR functions in the conversion of nucleobase, nucleoside and nucleotide derivatives of G to A nucleotides, and in maintaining the intracellular balance of A and G nucleotides.