The role of selected cytochrome P450 enzymes on the bioactivation of aflatoxin B1 by duck liver microsomes

Figures & data

Table 1.  Enzymatic parameters for selected P450 enzymatic activities in duck liver microsomes^a.

Substrate	Human orthologue activity	Responsible CYP450	K M (µM)	V max (nmol/mg microsomal protein/min)	Correlation coefficient for Michaelis–Menten kinetics
7-Ethoxyresorufin	7-Ethoxyresorufin O-deethylation	CYP1A1/2	1.84±0.17	0.26±0.05	≥0.98
Methoxyresorufin	Methoxyresorufin O-deethylation	CYP1A2	0.95±0.16	0.86±0.11	≥0.94
Coumarin	Coumarin 7-hydroxylation	CYP2A6	6.61±0.88	0.37±0.05	≥0.92
Nifedipine	Nifedipine oxidation	CYP3A4	32.6±3.27	5.12±0.54	≥0.95
^aEach value corresponds to the mean±standard error of six observations (three males and three females). No debrisoquinone 4-hydroxylase activity (CYP2D6) was detected.

Figure 1.  Effect of selected chemical inhibitors on cytochrome P450-mediated AFB1 epoxide production in duck liver microsomes. Each graph corresponds to six individual birds per experiment (three males and three females). Each graph header indicates the enzymatic activity affected by the inhibitor.

Figure 2.  Effect of selected chemical inhibitors on cytochrome P450-mediated AFB1 epoxide production in duck liver microsomes. Each bar corresponds to the mean±standard deviation of six observations per experiment (three males and three females). Each graph header indicates the enzymatic activity affected by the inhibitor. *Significantly different (P < 0.05) from control.

Figure 3.  AFB1 epoxidation versus model substrate enzymatic activity in duck liver microsomes (n = 12). The enzyme associated with the model enzymatic activity indicated in the y-axis is shown on top of each graph. A positive significant relationship (P < 0.05) was observed for all enzymatic activities tested.

Figure 4.  Protein blot of selected duck CYP450 orthologues. Lanes 1 to 6, bands obtained with six different samples of duck microsomes; lanes 7 to 9, microsomes containing cDNA-expressed human CYP450 enzymes as indicated in each graph. Molecular weight standards are shown with their corresponding molecular weight value.