Oxidation of xenobiotics by plant microsomes, a reconstituted cytochrome P450 system and peroxidase: a comparative study

The microsomal fraction from tulip bulbs (Tulipa fosteriana, L.) contains c ytochrome P450 (CYP3, EC 1.14.14.1) and peroxidase (EC 1.11.1.7.) enzymes c atalyzing the NADPH - and hydrogen peroxide - dependent oxidation of the xe nobiotic substrates, N-nitrosodimethylamine (NDMA), Nw-nitrosomethylaniline (NMA), aminopyrine and 1-phenylazo 2-hydroxynaphthalene (Sudan I), respect ively. Oxidation of these model xenobiotics has also been assessed in a rec onstituted electron-transport chain with a partially purified CYP fraction, phospholipid and isolated tulip NADPH:CYP reductase (EC 1.6.2.4.). Peroxid ase isolated from tulip bulbs (isoenzyme C) oxidizes these xenobiotics, too . Values of kinetic parameters (K-m, V-max), requirements for cofactors (NA DPH, hydrogen peroxide), the effect of inhibitors and identification of pro ducts formed from the xenobiotics by the microsomal fraction, partially pur ified CYP and peroxidase C were determined. These data were used to estimat e the participation of the CYP preparation and peroxidase C in oxidation of two out of the four studied xenobiotics (NMA, Sudan I) in tulip microsomes . Using such detailed study, we found that the CYP-dependent enzyme system is responsible for the oxidation of these xenobiotics in the microsomal fra ction of tulip bulbs. The results demonstrate the progress in resolving the role of plant CYP and peroxidase enzymes in oxidation of xenobiotics. (C) 2000 Elsevier Science Ltd. All rights reserved.