STIMULATION BY PARAQUAT OF MICROSOMAL AND CYTOCHROME P-450-DEPENDENT OXIDATION OF GLYCEROL TO FORMALDEHYDE

Glycerol can be oxidized to formaldehyde by microsomes in a reaction t hat is dependent on cytochrome P-450. An oxidant derived from the inte raction of H2O2 with iron was responsible for oxidizing the glycerol, with P-450 suggested to be necessary to produce H2O2 and reduce non-ha em iron. The effect of paraquat on formaldehyde production from glycer ol and whether paraquat could replace P-450 in supporting this reactio n were studied, Paraquat increased NADPH-dependent microsomal oxidatio n of glycerol; the stimulation was inhibited by glutathione, catalase, EDTA and desferrioxamine, but not by superoxide dismutase or hydroxyl -radical scavengers. The paraquat stimulation was also inhibited by in hibitors, substrate and ligand for P-4502E1 (pyrazole-induced P-450 is ozyme), as well as by anti-(P-4502E1) IgG. These results suggest that P-450 still played an important role in glycerol oxidation, even in th e presence of paraquat. Purified NADPH-cytochrome P-450 reductase did not oxidize glycerol to formaldehyde; some oxidation, however, did occ ur in the presence of paraquat. Reductase plus P-4502E1 oxidized glyce rol, and a large stimulation was observed in the presence of paraquat. Rates in the presence of P-450, reductase and paraquat were more than additive than the sums from the reductase plus P-450 and reductase pl us paraquat rates, suggesting synergistic interactions between paraqua t and P-450. These results indicate that paraquat increases oxidation of glycerol to formaldehyde by microsomes and reconstituted systems, t hat H2O2 and iron play a role in the overall reaction, and that paraqu at can substitute, in part, for P-450 in supporting oxidation of glyce rol. However, cytochrome P-450 is required for elevated rates of forma ldehyde production even in the presence of paraquat.