Simplified schematic of guanylate metabolic pathway and the proposed model. Enzymes are shown by ovals. Inhibitors of the pathway are indicated. IMP, inositol monophosphate; XMP, xanthosine monophosphate; GMP, guanosine monophosphate; GDP, guanosine diphosphate; GTP, guanosine triphosphate; ATP, adenosine triphosphate; IMPDH, inositol monophosphate dehydrogenase; GMPS, GMP synthase; GMPR, GMP reductase; MPA, mycophenolic acid; MMF, mycophenolate mofetil.