GMP Reductase 1 (GMPR) is a member of the IMPDH/GMPR family. GMPR exists as a homotetramer and catalyzes the irreversible NADPH-dependent deamination of GMP to IMP. It 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. GMP reductase gene expression may be regulated by MITF. At least two different alleles are known.