Xenobiotic-Metabolizing Enzyme Systems in Test Fish : V. Comparative Studies of Liver Microsomal Glucuronyltransferases

UDPG-glucuronyltransferase (GT) activities have been determined in the hepatic microsomes of fish species recommended by OECD for some (eco)toxicological tests. Due to the heterogeneity of this enzyme family, different chemicals were used as substrate: 4-nitrophenol (4NP), 4 methylumbelliferone (4MU), and 2- and 4-hydroxybiphenyl (2OHB and 4OHB). The 4NP-GT and 2OHB-GT activities of hepatic microsomes from all the species were linearly dependent on the substrate concentration (tested concentrations up to 2 and 0.5 mM, respectively). 4OHB-GT and 4MU-GT demonstrated different degrees of saturation in the range of substrate concentrations 0-0.5 mM and 0-0.3 mM, respectively. Specific activities ranged among the species usually within a factor of about 3. The highest ratios (up to 10) were occasionally found for 4MU-GT (between trout and golden orfe) and 20HB-GT (between guppy and carp, zebra fish, or trout). These results confirm that GT activities in fish are much lower than in mammals.