IMP dehydrogenase / GMP reductase, conserved site Synonym(s): Inosine-5'-monophosphate dehydrogenase, Inosinic acid dehydrogenase; Synonym(s): Guanosine 5'-monophosphate oxidoreductase <p>This entry contains two related enzymes IMP dehydrogenase and GMP reducatase. These enzymes adopt a TIM barrel structure.</p><p>IMP dehydrogenase (<db_xref db="EC" dbkey="1.1.1.205"/>) (IMPDH) catalyzes the rate-limiting reaction of <i>de novo</i> GTP biosynthesis, the NAD-dependent reduction of IMP into XMP [<cite idref="PUB00002466"/>].<reaction>Inosine 5-phosphate + NAD⁺ + H₂O = xanthosine 5-phosphate + NADH</reaction>IMP dehydrogenase is associated with cell proliferation and is a possible target for cancer chemotherapy. Mammalian and bacterial IMPDHs are tetramers of identical chains. There are two IMP dehydrogenase isozymes in humans [<cite idref="PUB00002609"/>]. IMP dehydrogenase nearly always contains a long insertion that has two CBS domains within it.</p><p>GMP reductase (<db_xref db="EC" dbkey="1.7.1.7"/>) catalyzes the irreversible and NADPH-dependent reductive deamination of GMP into IMP [<cite idref="PUB00000471"/>].<reaction>NADPH + guanosine 5-phosphate = NADP⁺ + inosine 5-phosphate + NH₃ </reaction>It converts nucleobase, nucleoside and nucleotide derivatives of G to A nucleotides, and maintains intracellular balance of A and G nucleotides.</p>