Category: drug_metabolism
Phase-2 conjugating enzymes attach polar groups to phase-1 oxidized metabolites (or directly to parent drugs), dramatically increasing water solubility for biliary or renal excretion. UGT (UDP-glucuronosyltransferase) — major; bilirubin + many drugs (UGT1A1 deficiency = Gilbert syndrome benign hyperbilirubinemia + atazanavir-induced jaundice; Crigler-Najjar severe form). SULT (sulfotransferase) — major for acetaminophen at therapeutic doses, hormones. GST (glutathione-S-transferase) — major for reactive metabolites (NAPQI from acetaminophen → GST → mercapturate excretion). NAT (N-acetyltransferase, NAT2) — isoniazid + sulfonamides; slow/fast acetylator phenotypes (NAT2 polymorphism affects INH toxicity). Methylation (COMT, HNMT) + acetylation (NAT) close the major phase-2 axes.