Recombinant enzyme prepared from insect cells infected with baculovirus containing human UGT1A1 cDNAs
UDP-glucuronosyltransferases (UGT) represent the major phase II drug metabolism pathway in human. UGT enzymes catalyze the transfer of glucuronic acid (derived from UDPGA co-factor) to xenobiotics and endogenous substrates having nucleophilic acceptor groups, making them more polar and readily excreted in urine or bile. To date, at least 18 human UGT enzymes have been cloned and sequenced. Like the P450 enzymes, UGTs possess broad and overlapping substrate specificities. Clinically relevant drug interactions have been identified for UGT isoforms, leading regulatory agencies (FDA) to require drug interaction testing for compounds showing significant UGT metabolism.
UGT1A1 is abundant in liver and is responsible for the metabolism of numerous drug substrates. UGT1A1 is responsible for the in vivo glucuronidation of bilirubin, a toxic byproduct of heme. It is a highly polymorphic isoform, with at least 100 mutations identified, some leading to the complete absence of activity resulting in severe cases of hyperbilirubinium. UGT1A1 is selective for the glucuronidation of ß-estradiol, etoposide and bilirubin.