UDP-GLUCURONOSYLTRANSFERASE KINETICS FOR 3-TRIFLUOROMETHYL-4-NITROPHENOL (TFM) IN FISH

Studies were conducted to address glucuronidation of 3-trifluoromethyl -4-nitrophenol (TFM) in sea lampreys Petromyzon marinus, channel catfi sh Ictalurus punctatus, rainbow trout Oncorhynchus mykiss, and bluegil ls Lepomis macrochirus. The ability of these species to biotransform T FM was investigated by determining the kinetics of UDP-glucuronyltrans ferase (UDPGT; also known as glucuronosyltransferase) in vitro from he patic microsomal preparations. Maximal velocity (V(max) nmol/min.mg) f or UDPGT activity toward TFM was significantly greater (P < 0.05) in b luegills (1.52), rainbow trout (1.82), and channel catfish (1.46) than in sea lampreys (0.68). Binding affinities (K(m)) of UDPGT for TFM va ried significantly among species in the following order: bluegill (58 muM) > rainbow trout (97 muM) > channel catfish (172 muM) > sea lampre y (261 muM). Analysis of V(max)/K(m) ratios, a measure of enzyme effic iency (nmol/min.mg.muM TFM), indicated that the efficiency of UDPGT ac tivities in all species examined was influenced more by binding affini ty (K(m)) than by the V(max) of the reaction. These calculated ratios were progressively lower for species that were previously reported to be more sensitive to aqueous TFM (i.e., to have lower LC50s, TFM conce ntrations lethal to half the test fish). Sea lampreys appear to have r elatively low UDPGT activity and binding affinity for phenolic substra tes. This, in part, may account for the sensitivity of the sea lamprey to aqueous TFM.