A high-molecular regulator of 7-ethoxyresorufin- O-deethylase activity in fish

The postmicrosomal protein supernatant (PMSPS) of bream and rainbow trout liver homogenates inhibits the 7-ethoxyresorufin- O-deethylase (EROD) activity of the microsomal protein (MSP) preparation of liver cells in fish species like bream, perch, pike, roach and rainbow trout, of mammals like the marmoset and of the microsomal preparation of crayfish hepatopancreas. In the crayfish Orconectes, pentoxyresorufin- O-depentylase (PentROD) is also inhibited, while benzoxyresorufin- O-debenzylase (BenzROD) is activated. The inhibiting substance is a heat-, acid- and ethanol-sensitive protein with a relative molecular weight of 185 kDa. The mode of inhibition is non-competitive. Gel filtration on Sephadex G-150 resolves the PMSPS into EROD-inhibiting and -activating fractions. The inhibitory activity is not impaired by the addition of protease inhibitors like leupeptin or PMSF. One-year-old rainbow trout reared under controlled conditions in a net cage can be classified into Class 1 animals with low inhibitory activity and high EROD activity and Class 2 animals with high inhibitory activity and low EROD activity. These ratios were found in free-living roach, too. Of the species raised in outdoor conditions, perch display the lowest inhibitory activity and the highest EROD activity. The inhibitory activity of bream is medium and the one of roach is highest. The EROD activity of these two species is within the same low range. In bream, the inhibitory activity, as well as the EROD activity, seems to be negatively correlated to the conditions index and/or positively to the pollution of the home range of the samples. The inhibitory, as well as the EROD activity of bream is higher in the second half of the year. The maximum inhibitory activity of bream is higher in the second half the maximum enzyme activity.