Mixed-function oxygenase activity and benzo[a]pyrene metabolism in the barnacle Balanus eburneus (Crustacea: Cirripedia)

Abstract

1. Microsomal cytochrone P-450-dependent mixed-function oxygenases were observed in digestive gland, intestine, cirri and gonad of the cirriped crustacean (barnacle) Balanus eburneus. 2. Levels of the microsomal electron transport components cytochrome P-450, cytochrome b 5, NADPH-cytochrome c reductase and NADH-cytochrome c reductase in B. eburneus were lower than found in vertebrate liver, but like those seen in some decapod crustaceans. 3. The levels of benzo[a]pyrene hydroxylase activity were maximal at pH 7.5 and at temperatures between 15 and 30°C. Maximal activities ranged between 2 and 43 pmol 3-hydroxybenzo[a]pyrene min/mg microsomal protein as measured with a fluorescence assay. Activities were higher in summer than in winter. 4. Substrate saturation curves obtained for benzo[a]pyrene were hyperbolic, with none of the complexity seen in vertebrates. The K m S for benzo[a]pyrene metabolism in digestive gland and intestine were 6–7 × 10 −7 M. 5. Compounds eluting with 3-hydroxybenzo[a]pyrene in HPLC analyses constituted almost 60% of metabolites formed by barnacle digestive gland microsomes. 9-hydroxybenzo[a]pyrene, 7,8-dihydrodiol and 9,10-dihydrodiol were formed more slowly. 6. Benzo[a]pyrene hydroxylase activity in tissue microsomes from untreated animals was inhibited more than 50% by 10 −4 M 7,8-benzoflavone. 7. Cytochromes P-450 in barnacles might be functionally related to the status of hormones regulating development and reproduction.