Hepatic microsomal monooxygenases of sea birds

Abstract

The present study was part of an investigation into the biochemical basis for the strong bioaccumulation of persistent organochlorine pollutants by many fish-eating birds. Hepatic microsomal monooxygenase was assayed in six species of sea birds from British and Irish coastal waters using as substrates the organochlorine compounds aldrin (1,2,3,4,10,10hexachloro1,4,4a,5,8,8a-hexahydro-exo1,4-endo-5,8-dimethanonaphthalene) and HCE (1,2,3,4,9,9-hexachloro-l,4,4a,5,6,7,8,8a,octahydroexo-7,8-epoxy-l,4-methanonaphthalene). The razorbill (Alca torda), guillemot (Uria aalge), shag (Phalacrocorax aristotelis), cormorant (Phalacrocorax carbo) and Manx shearwater (Puffinus puffinus) had much lower activities than the puffin (Fratercula arctica). When these values were compared with other data from the literature on a scale of relative activity, the high activities of the puffin were similar to those of mammals and certain omnivorous or herbivorous birds, whereas the low activities of the other five species were similar to those of fish (Walker & Knight, 1981). In the three auks, enzyme activities were highly variable and resolved into two or more peaks when frequency diagrams were plotted. This was not so with the shag. In the razorbill, individuals of low activity (Group I) were compared with individuals of higher activity (Group II) (Knight & Walker, 1982). Individuals from Group II had, on average, 5.6-8.5-fold higher monooxygenase activity at saturating substrate concentrations than did Group I, although there was only a 1.6-fold difference in microsomal cytochrome P-450 between the groups. Lineweaver-Burke plots for