Cytochrome P4501 AI is a major isoenzyme in fish monooxygenase system which is induced by polycyclic aromatic hydrocarbons (PAHs) compounds. In this research, the inducing effect of p-naphtoflavone and its catalytic properties was studied in Huso huso liver. Fish were given ip injection of p-naphthoflavone at three different doses. The enzyme activity was measured with de-ethylation of ethoxyresorufin reaction (EROD) by flourometery method and relative amount of induced proteins were determined using polyacrylamid del electrophoresis (SDS-PAGE). The results showed that EROD activity in the microsomal fraction of the treated fish was 15-26 folds that of the control group. Optimum activity of this enzyme was observed at 20-25 degrees centivade. The maximum enzyme activity was seen in the precence of 180 micrograms of microsomai protein and 1.5311M of 7-ethoxyresorufin. SDS-PAGE of microsomal protein pattern in the treated fish revealed a protein with molecular mass 58+1 KDa translating to cytochrome P4501A. We conclude that the p-naphtoflovone in fish liver can induce cytochrome P4501A gene and increase its biosenthysis leading to raised enzyme activity in EROD reaction
