3-Methylcholanthrene does induce mixed function oxidase activity in hepatopancreas of spiny crab Maja crispata.

1. Type II inducers (7,8-benzoflavone, benzo(a)-pyrene and 3-methylcholanthrene) as well as Aroclor 1254, significantly increase benzo(a)pyrene monooxygenase activity in crab hepatopancreas while type I inducer (phenobarbital) does not enhance benzo(a)pyrene monooxygenase activity. 2. 3-methylcholanthrene and benzo(a)pyrene treatment of crabs significantly increase cytochrome P-450 content. 3. Benzo(a)pyrene monooxygenase induction in hepatopancreas of 3-methylcholanthrene treated crabs was inhibited by simultaneous treatment with cycloheximide but not by actinomycin D. 4. Actinomycin D insensitivity can be explained involving a regulatory pattern of induction on the posttranscriptional and/or translational, rather than transcriptional level.