Catalyzes the conversion of inosine 5'-phosphate (IMP) to xanthosine 5'-phosphate (XMP), the first committed and rate-limiting step in the de novo synthesis of guanine nucleotides, and therefore plays an important role in the regulation of cell growth. In contrast to the other IMPDH alleles IMD3 and IMD4, the enzymatic activity of IMD2 seems to be intrinsically drug resistant. H2O + IMP + NAD(+) = H(+) + NADH + XMP Mycophenolic acid (MPA) is a non-competitive inhibitor that prevents formation of the closed enzyme conformation by binding to the same site as the amobile flap. In contrast, mizoribine monophosphate (MZP) is a competitive inhibitor that induces the closed conformation. MPA is a potent inhibitor of mammalian IMPDHs but a poor inhibitor of the bacterial enzymes. MZP is a more potent inhibitor of bacterial IMPDH. Purine metabolism; XMP biosynthesis via de novo pathway; XMP from IMP: step 1/1. Homotetramer. Seems to be able to form heterotetramers composed from more than 1 of the 3 IMPDH gene products (IMD2-4). Induced by MPA resulting in resistance to the drug. Repressed by nutrient limitation. Present with 7870 molecules/cell in log phase SD medium. Belongs to the IMPDH/GMPR family.