THE EFFECT OF BETA-NAPHTHOFLAVONE AND PHENOBARBITAL ON UDP-GLUCURONOSYLTRANSFERASE IN KING SALMON (ONCORHYNCUS-TSHAWYTSCHA)

Groups of king salmon, under anesthesia with MS222, received either a single injection of 100 mg/kg body weight (beta-naphthoflavone) or two injections at the same ratio (phenobarbital) three weeks prior to sacrifice. Controls received the appropriate vehicle only. Hepatic microsomes were prepared and UDP-glucuronosyltransferase (UDPGT) activities toward 4-nitrophenol, 1-naphthol and bilirubin were assayed Activities toward 4-nitrophenol and 1-naphthol in beta-naphthoflavone-treated fish were increased 1.81- and 2.15-fold respectively. Bilirubin UDPGT activity was not detectable. No induction by phenobarbital was observed. Kinetic analyses of 4-nitrophenol activity with respect to UDP-glucuronic acid (UDPGA) and 4-nitrophenol concentrations were carried out. K(m) and V(max) values for UDPGA were 1.7 mm and 1.1 units/mg, respectively. Between 0.05 and 4.0 mm 4-nitrophenol the reaction velocity increased linearly, indicating a lack of affinity for this substrate.