CHARACTERIZATION AND DETERMINATION OF THE ACTIVITY OF BILIARY BETA-GLUCURONIDASE IN RATS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 93  (6) , 916-925
Abstract
.beta.-Glucuronidase [EC 3.2.1.31] activity determined in 100 diluted bile samples from 12 rats with bile duct fistula by using phenolphthalein glucuronide as substrate incubated at 56.degree. C and pH 6 was 636 .+-. 650 (mean .+-. S.D.) modified Sigma units/ml. The enzyme had an optimal pH of 6.0 and was inhibited slightly by cholate but markedly by chenodeoxycholate and deoxycholate. The biliary .beta.-glucuronidase had low activity under normal physiologic condition because of the high pH (8.1) and high bile salt content (20 .mu.mol/ml) of the bile. The enzyme kinetic studies revealed that the direct bilirubin was a competitive inhibitor to phenolphthalein glucuronide for the enzyme. The affinity of the former to the enzyme was 163 times that of the latter. The studies provided a method for measuring the true activity of biliary .beta.-glucuronidase (Vmax) devoid of interfering factors by measuring the enzyme velocity (v) in the diluted bile with at least 5 different concentrations of substrate (s). The plotting of (1/v) vs. (1/s) should yield the y intercept or (1/Vmax).