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  • Title: Isolation and characterization of hyodeoxycholic-acid: UDP-glucuronosyltransferase from human liver.
    Author: Matern H, Lappas N, Matern S.
    Journal: Eur J Biochem; 1991 Sep 01; 200(2):393-400. PubMed ID: 1909626.
    Abstract:
    The enzyme hyodeoxycholic-acid: UDP-glucuronosyltransferase was purified about 230-fold from a solubilized human liver microsomal preparation utilizing anion-exchange chromatography, ampholyte-displacement chromatography and UDP-hexanolamine--Sepharose affinity chromatography. The homogeneity of the final enzyme preparation was judged by two criteria: the appearance of a single band of Mr 52000 in SDS/PAGE; the elution of a single peak in reversed-phase FPLC. The isolated enzyme catalyzed the glucuronidation of the 6 alpha-hydroxy bile acids hyodeoxycholic and hyocholic acids, and of the steroid hormone estriol, with a ratio of relative reaction rates of 13:1:2.7. UDP-glucuronosyltransferase activities toward the 3 alpha-hydroxy bile acid lithocholic acid, androsterone, testosterone, bilirubin and p-nitrophenol were not detectable in the pure enzyme preparation and were shown to be separated from enzyme activity toward hyodeoxycholic acid during ampholyte-displacement chromatography and/or UDP-hexanolamine--Sepharose affinity chromatography. Two-substrate kinetic analysis of hyodeoxycholic-acid-conjugating activity gave a sequential mechanism with apparent Km values of 12 microM and 4 microM for hyodeoxycholic acid and UDP-glucuronic acid, respectively. Phospholipids were required for reconstitution of maximal activity toward hyodeoxycholic acid. Phosphatidylcholine was the most effective activator of enzyme activity.
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