Purification and partial characterization of rat liver bilirubin glucuronoside glucuronosyltransferase

• Published in: The Journal of biological chemistry Vol. 254; no. 17; pp. 8336 - 8339
• Main Authors: Chowdhury, J R, Chowdhury, N R, Bhargava, M M, Arias, I M
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 10-09-1979
• Subjects: Animals; Bilirubin - metabolism; Glucuronosyltransferase - isolation & purification; Glucuronosyltransferase - metabolism; Kinetics; Liver - enzymology; Male; Molecular Weight; Rats
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)86894-1

Bilirubin glucuronoside glucuronosyltransferase (EC 2.4.1.95) converts bilirubin monoglucuronide to bilirubin diglucuronide
and is concentrated in plasma membrane-enriched fractions of rat liver homogenates. The enzyme was purified 2,000-fold to
homogeneity from rat liver. The pI of the enzyme is 7.9 +/- 0.2. The enzyme has a molecular weight of 160,000 and is an oligomer
of 28,000 dalton subunits. Km for purified enzyme was 35 microM and Vmax was 2.2 mumol of bilirubin diglucuronide formed/min/mg
of protein. Freshly biosynthesized bilirubin monoglucuronide was injected intravenously into homozygous Gunn rats which had
bile duct cannulation. Gunn rats lack UDP-glucuronate glucuronyltransferase activity (EC 2.4.1.17), have normal bilirubin
glucuronoside glucuronosyltransferase activity, cannot form bilirubin monoglucuronide in vitro or in vivo, and do not excrete
bilirubin glucuronides after intravenous injection of unconjugated bilirubin. Within 1 h, approximately 75% of the injected
conjugated bilirubin was recovered in bile, of which 20% consisted of bilirubin diglucuronide. These results indicate that
bilirubin glucuronide glucuronosyltransferase catalyzes conversion of bilirubin monoglucuronide to diglucuronide in vivo.