Tissue and subcellular distribution of enzyme activities of mixed-function oxygenase and Benzo[a]Pyrene metabolism in the common mussel Mytilus edulis L.

Abstract

Abstract A survey of the tissue and subcellular distribution of some enzyme activities of mixed-function oxygenase (MFO) and benzo [a] pyrene (BP) metabolism in Mytilus edulis has been carried out. Subcellular fractions were characterized by marker enzymes (pyruvate kinase, β-N-acetylglucoseaminidase, succinic dehydrogenase and glycose-6-phosphatase) and electron microscopy. The tissues examined in male and female mussels were the digestive gland, gills, mantle, posterior adductor muscle, foot, ‘rest’ fraction and blood cells. Evidence was obtained that in the female digestive gland in particular a signifant fraction of the microsomes co-sedimented with the mitochondria at 12 000 × g and some solubilization of the endoplasmic reticulum also occurred during homogenization and extraction. MFO activities and cytochromes were localized in the microsomes. Cytochrome P-450 was present only in the digestive gland and the P-450-associated activities were highest in this tissue. In contrast cytochrome b5 was also present in the gills and mantle. The activities were higher in the digestive gland microsomes of female mussels than of males and were in females (means ± SEM, n = 4): 7.5 ± 0.7 (glucose-6-phosphate dehydrogenase), 930.2 ± 54.6 (NADH-ferricyanide reductase), 156.5 ± 9.5 (NADH-cytochrome c reductase) and 18.4 ± 4.6 (NADPH-cytochrome c reductase) (all in nmol min−1 mg−1 protein at 25°C); 31.0 ± 3.9 (BP hydroxylase, pmol min−1 mg−1 protein at 25°C); 75.5 ± 11.7 (b5) and 134 ± 64 (P-450) (in pmol mg−1 protein and both the pooled material of both sexes, n = 4). Digestive gland microsomal BP hydroxylase activity was partially inhibited by carbon monoxide, SKF-525A and α-naphtoflavone. Based on this evidence and an observed relationship between microsomal BP hydroxylase and NADPH-cytochrome c reductase activities, it is concluded that a cytochrome P-450 mediated MFO system is present in mussels.