ABSTRACT
The crab mixed-function oxygenase (MFO) system is similar to that in vertebrate systems since it is associated with the microsomal fraction and requires phospholipid, cytochrome P-450, and NADPH-cytochrome P-450 reductase for activity. The cytochrome P-450-mediated MFO system was detected in polychaete annelids. Several experiments were conducted to determine the responses of the MFO system to organic pollutants in the food. Low MFO activity in the hepatopancreas of many marine crustaceans is due to inhibition by digestive juices released during homogenization of the tissues. Molecular weight determinations by SDS-polyacrylamide gel electrophoresis indicated a major band at 54,000 daltons for both male and female cytochrome P-450. The binding of numerous organic compounds to oxidized cytochrome P-450 causes spectral changes in the Soret region for the heme prosthetic group. Electron paramagnetic resonance spectroscopy has shown type I binding to result from shifting equilibrium of the spin states of ferric iron in cytochrome P-450 from low to high spin.
