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2141125 
Journal Article 
Mixed function oxygenase activity in the blue crab, Callinectes sapidus: Characterization of enzyme activity from stomach tissue 
Singer, SC; March P E, , JR; Gonsoulin, F; Lee, RF 
1980 
Yes 
Comparative Biochemistry and Physiology - Part C: Comparative Pharmacology
ISSN: 0306-4492 
HEEP/80/10907 
65 
2 
129-134 
eng 
HEEP COPYRIGHT: BIOL ABS. The mixed function oxygenase (MFO), arylhydrocarbon hydroxylase (AHH), was characterized from stomach tissue of blue crab. Maximal enzyme activity was attained at 30? C and pH 7.5 in the presence of NADPH, O2 and Mg when benzo(a)pyrene was employed as the substrate. Components of the MFO system, cytochrome P-450 and phospholipid, were necessary for maximal activity by use of cytochrome P-450 inhibitors, detergents, inhibition by phospholipase c and spectral observations of cytochrome P-420. The remaining component, NADPH cytochrome P-450 reductase, was assayed using cytochrome c as the electron recipient. Four other polycyclic aromatic compounds were modified (phenanthrene, benz(a)anthracene; 7,12-dimethylbenz(a)anthracene and 5,6-chysene) in addition to benzo(a)pyrene under in vitro assay conditions. The major products of benzo(a)pyrene metabolism by stomach tissue were the phenols, 3-hydroxybenzo(a)pyrene and 9-hydroxybenzo(a)pyrene with minor amounts of the diols, probably trans-4,5-dihydrodiol benzo(a)pyrene and trans-7,8-dihydrodiol benzo(a)pyrene. Two other mixed function oxygenase activities, 7-ethoxycoumarin de-ethylase and 7-ethoxyresorufin dealkylase, were also present in stomach microsomes. No increase in AHH activity occurred after injection of benz(a)anthracene or phenobarbital or feeding food contaminated with benz(a)anthracene. Inhibition of AHH activity by low concentrations of 7,8-naphthoflavone (84% at 10-6 M) and lack of induction suggested important differences between the AHH of crabs and other animals.