Channel catfish liver monooxygenases. Immunological characterization of constitutive cytochromes P450 and the absence of active flavin-containing monooxygenases.

Multiple drugs and pesticides are used in the aquaculture of channel catfish in the Southeastern United States. However, little is known regarding the enzymatic metabolism of these chemicals in the fish. Western blots, utilizing polyclonal antibodies raised against five purified rainbow trout liver cytochrome P450 enzymes, revealed at least two protein bands that were approximately 50 kDa (CATL-1) and 53 kDa (CATL-2). Anti-trout LMC3 and LMC4 only hybridized with the 53 kDa protein, whereas anti-trout LMC1, LMC2, and LMC5 recognized both proteins. Cytochrome P450-catalyzed activities (testosterone and progesterone hydroxylases) associated with LMC1 and LMC5 were also found in catfish liver microsomes. These data suggest that at least two constitutive forms of cytochrome P450 are present in the liver of juvenile channel catfish. Western blots utilizing antibodies raised against rabbit-lung flavin-containing monooxygenases (FMO) showed hybridization with two proteins from rainbow trout liver microsomes, but no cross-reaction with microsomes from catfish liver. N,N,-Dimethylaniline N-oxidase and methimazole oxidase were observed in microsomes from trout, but were absent in catfish liver microsomes prepared in three different laboratories. Consequently, FMO do not appear to be present in liver microsomes from channel catfish or they are rapidly degraded during tissue homogenization.