Acceptor-specific glucuronyl transfer catalyzed by beta-glucuronidase.
Highly purified rat liver microsomal or lysosomal beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31) catalyzes the specific transfer of glucuronly residues from phenyl-beta-D-[U-14C]glucuronide to acceptor sugars. Specificity requirements of acceptor sugars are found to be: pyranose structure, 4C1-conformation and equatorial position of C2 and C3 hydroxyl groups or pyranose structure, 1C4-conformation and equatorial position of C3 and C4 hydroxyl groups. The acceptor capacities of 30 monosaccharides and glycosides including di- and tri- saccharides conform to this prinicple. The specificity of the beta-glucuronidase catalyzed glucuronyl transfer is proved by the exclusive formation of beta-glucuronly (1--3)glycosidic linkages. Glucuronly transfer rates increase with increasing donor substrate and increasing acceptor sugar concentration. In the presence of 1 M acceptor sugar the ratio of the transfer rate to the rate of enzymatic hydrolysis is about 2:1. An 'acceptor substrate binding site' on the surface of the beta-glucuronidase molecule which brings the C3 hydroxyl function of the acceptor sugar close enough to the C1 atom of the glucuronyl residue, is postulated.
D000818:Animals; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D004187:Disaccharides; D005965:Glucuronates; D005966:Glucuronidase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D009005:Monosaccharides; D051381:Rats; D013379:Substrate Specificity; D014312:Trisaccharides
D004187:Disaccharides; D005965:Glucuronates; D009005:Monosaccharides; D014312:Trisaccharides; D005966:Glucuronidase