Distribution of UDPglucuronosyltransferase in rat tissue.

Abstract

UDPglucuronosyltransferase [UDPglucuronate 13-D-glucuronosyltransferase (acceptor-unspecific), EC 2.4.1.17] is a group of enzymes with distinct but partially overlapping substrate specificity. A rabbit antiserum raised against one purified rat liver UDPglycuronosyltransferase isoform was specific for UDPglucuronosyltransferase and recognized all transferase isoforms by immunodiffusion or immunotransblot analysis. The transferase activity toward all substrates was immunoabsorbed from solubilized rat liver microsomes by IgG purified from the antiserum. The purified IgG was used for immunocytochemical localization of UDPglucuronosyltransferase in rat liver, jejunum, kidney, and adrenal gland. In the liver, UDPglucuronosyltransferase was present exclusively in hepatocytes and was uniformly distributed within all zones of the hepatic lobule. In the jejunum, the transferase was present exclusively in the epithelial cells and showed a progressive increase in concentration from the crypt to the villar tip. In the kidney, the greatest concentration of the transferase was observed in the epithelial cells of the proximal convoluted tubule. Adrenal medullary cells showed intense immunocytochemical staining; the zona glomerulosa and the zona reticularis of the adrenal cortex were more intensely stained than the zona fasciculata. By light microscopy, UDPglucuronosyltransferase was found in the endoplasmic reticulum and nuclear envelope of all the four organs; this was confirmed in the hepatocyte by electron microscopy. The transferase was not observed in mitochondria, Golgi apparatus, lysosomes, peroxisomes, and plasma membrane, even after 3-to 4-fold induction of various substrate-specific UDPglucuronosyltransferase activities.

Induction of central tolerance by intrathymic inoculation of adenoviral antigens into the host thymus permits long-term gene therapy in Gunn rats.

“…Gunn rats are an animal model of human CriglerNajjar syndrome type I. Because hepatic glucuronidation is essential for disposition of bilirubin, Gunn rats and patients with Crigler-Najjar syndrome type I have lifelong unconjugated hyperbilirubinemia, resulting in brain damage (19)(20)(21). CriglerNajjar syndrome is potentially lethal, and liver transplantation is the only definitive treatment (21).…”

“…We introduced the gene for human bilirubin-UGT-1 (hBUGT 1 ), the only enzyme that significantly contributes to bilirubin glucuronidation in human liver, into Gunn rats, using a recombinant adenoviral vector (5). The advantage of using Gunn rats for these experiments is that the BUGT expression can be evaluated by monitoring serum bilirubin levels (18)(19)(20). In addition, excretion of bilirubin glucuronides in bile provides unequivocal evidence of hBUGT 1 expression in vivo.…”

Tissue mRNA Expression of the Rat UDP-Glucuronosyltransferase Gene Family

“…2 ) are phase II biotransformation enzymes localized to the endoplasmic reticulum (Chowdhury et al, 1985). UGTs catalyze the conjugation of glucuronic acid to a broad spectrum of endobiotic and xenobiotic substrates with diverse chemical structures.…”

Isolation and characterization of multiple forms of rat liver UDP-glucuronate glucuronosyltransferase

“…Supportive evidence for multiplicity of UDP-glucuronosyltransferases came from chromatographic separation of two (Burchell, 1978;Bock et al, 1979;Roy Chowdhury et al, 1983) or three forms of the enzyme with distinct substrate specificities from rat livermicrosomes. However, antisera raised against one form of purified rat liver UDP-glucuronosyltransferase react with all forms of rat liver UDP-glucuronosyltransferases Roy Chowdhury et al, 1983, 1985, and thus the structural multiplicity of rat liver UDP-glucuronosyltransferases has not been established. Identical proteins could possibly be chromatographically separated and exhibit functional difference because of different lipid or detergent content.…”