A plant metabolic activation system from Persea americana with cytochrome P450-dependent and peroxidase activities

Abstract

Microsomal fractions from different tissues of various plants (potato, cauliflower, aubergine, avocado pear, courgette, cucumber, banana, kiwi and strawberry) were prepared and their content of cytochrome P-450 (cyt-P450) determined. A S117 fraction from Persea americana (avocado pear) presented the highest content of cyt-P450. As a consequence of these data, we have developed and characterized this fraction as a plant metabolic activation system. The P. americana S117, used in this work, contains 0.75 ± 0.04 mg of protein per ml, 0.788 ± 0.078 nmol of cyt-P450 per mg of protein and has a peroxidase activity of 0.036 ± 0.005 (nmol tetraguaiacol/μg protein/min). The P. americana cyt-P450 remained stable during at least 60 days, stored at −80°C. This fraction activated 2-aminofluorene to a mutagenic product in S. typhimurium TA98, while it had no effect on the benzo[ a]pyrene activation. The treatment of the P. americana S117 with CO, the addition of diethyldithiocarbamate (DETC) or the absence of a NADPH-generating system in the activation mix, produced a partial inhibition of the 2-aminofluorene activation. Both peroxidase activity and a cyt-P450-dependent activity are assumed to be involved in the activation of this chemical mediated by P. americana S117.