Distribution of UDPglucuronosyltr (tissue distribution/intracellular distribution/immunocytochemistry)

UDPglucuronosyltransferase (UDPglucuro- nate j3-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 rec- ognized all transferase isoforms by immunodiffusion or im- munotransblot 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 UDP- glucuronosyltransferase in rat liver, jejunum, kidney, and adrenal gland. In the liver, UDPglucuronosyltransferase was present exclusively in hepatocytes and was uniformly distrib- uted 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 ap- paratus, lysosomes, peroxisomes, and plasma membrane, even after 3- to 4-fold induction of various substrate-specific UDPglucuronosyltransferase activities.