title: The properties of uridine diphosphate glucuronyltransferase(s) which catalyse the synthesis of steroid glucuronides in microsomal fractions from guinea-pig liver.
abstract: The properties of the UDP-glucuronyltransferase(s) of guinea-pig liver that catalyse the synthesis of steroid glucuronides were examined. There are many similarities between apparently different substrate-specific forms of these enzymes in that all are activated by bivalent metal ions, and all contain at least 2 thiol groups important for enzyme activity. On the other hand, there are significant differences between the enzymes conjugating steroids and those conjugating non-steroids. Only the latter are activated by UDP-N-acetylglucosamine, which enhances their relatively poor affinity for UDP-glucuronic acid. The steroid-conjugating forms of UDP-glucuronyltransferase are not activated by UDP-N-acetylglucosamine and have relatively high apparent affinities for UDP-glucuronic acid. The rate of glucuronidation of testosterone was inhibited by treatment with phospholipase A. Treatment with cholate or Triton X-100 did not enhance the rates of glucuronidation of any steroid tested. The data indicate several similarities between different forms of UDP-glucuronyltransferase, suggesting that there is a large family of related proteins. At the same time there are important differences in the parameters that modulate the rates of different glucuronidation reactions.
mesh_terms: D000818:Animals; D004958:Estradiol / Q000378:metabolism; D004970:Estrone / Q000378:metabolism; D005965:Glucuronates / Q000096:biosynthesis*; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D006168:Guinea Pigs; D008345:Manganese / Q000494:pharmacology; D008634:Mersalyl / Q000494:pharmacology; D008862:Microsomes, Liver / Q000032:analysis / Q000187:drug effects / Q000201:enzymology*; D009596:Nitrophenols / Q000378:metabolism; D010740:Phospholipases / Q000494:pharmacology; D011092:Polyethylene Glycols; D013739:Testosterone / Q000378:metabolism; D014535:Uridine Diphosphate Glucuronic Acid / Q000032:analysis; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000494:pharmacology
chemical_list: D005965:Glucuronates; D012739:Gonadal Steroid Hormones; D009596:Nitrophenols; D014535:Uridine Diphosphate Glucuronic Acid; D004970:Estrone; D011092:Polyethylene Glycols; D013739:Testosterone; D008345:Manganese; D004958:Estradiol; D014537:Uridine Diphosphate N-Acetylglucosamine; D008634:Mersalyl; D014453:Glucuronosyltransferase; D010740:Phospholipases