Mechanism of inhibition of purified leaping mullet ( liza saliens ) NADPH‐cytochrome P450 reductase by toxic metals: Aluminum and thallium

Abstract Aluminum and thallium may reach life‐threatening levels in aquatic systems in the near future because of their extensive use in various industrial fields. It is therefore important to study the mechanism of toxicity of aluminum and thallium on fish enzymes. To this aim, the effects of aluminum and thallium on the activity of purified leaping mullet ( Liza saliens ) cytochrome P450 reductase, an essential component of the important cytochrome P450 system, have been studied. Results indicated that both metal ions strongly inhibited the NADPH‐cytochrome P450 reductase. The IC 50 values of AlCl 3 and TlCl 3 were estimated to be 34 μM and 3 μM, respectively. The Lineweaver–Burk plot and Dixon plot revealed that both metal ions noncompetitively inhibited the purified mullet cytochrome P450 reductase. The K i values of Al 3+ and Tl 3+ were calculated from Dixon plots as 8.9 and 5.6 μM, respectively. The inhibitory effects of Al 3+ and Tl 3+ on purified cytochrome P450 reductase were partially recovered by 1 mM EDTA. Additionally, tin and magnesium were shown to have no apparent effect on purified mullet cytochrome P450 reductase. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:340–3347, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20200