UGT enzyme

UGT enzymes are the body's labeling machines for glucuronidation — the workers that take a sugar tag and stick it onto drugs and waste molecules so they can be shipped out. Where the cytochrome P450 family dominates the oxidative side of metabolism, the UGT family dominates this major conjugation route.

Their full name is UDP-glucuronosyltransferase. Each UGT transfers glucuronic acid from the activated cofactor UDP-glucuronic acid onto a nucleophilic group on the substrate — a hydroxyl, carboxyl, amine, or thiol. Like the P450s, UGTs are a family of related isoforms with overlapping but distinct substrate preferences, and they sit mainly in the endoplasmic reticulum membrane of the liver and gut.

UGTs handle a large share of drug elimination and of endogenous housekeeping, including the glucuronidation of bilirubin; an inherited deficiency in one UGT isoform causes the harmless jaundice of Gilbert's syndrome. Because they can be inhibited or induced and vary genetically between people, UGTs are a real source of variability and drug interactions — less famous than the P450s but increasingly important to assess in drug development.