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 that is dependent on cytochrome P-450. An oxidant derived from the interaction of H2O2 with iron was responsible for oxidizing the glycerol, with P-450 suggested to be necessary to produce H2O2 and reduce non-haem iron. The effect of paraquat on formaldehyde production from glycerol and whether paraquat could replace P-450 in supporting this reaction were studied. Paraquat increased NADPH-dependent microsomal oxidation 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 inhibitors, substrate and ligand for P-4502E1 (pyrazole-induced P-450 isozyme), as well as by anti-(P-4502E1) IgG. These results suggest that P-450 still played an important role in glycerol oxidation, even in the presence of paraquat. Purified NADPH-cytochrome P-450 reductase did not oxidize glycerol to formaldehyde; some oxidation, however, did occur in the presence of paraquat. Reductase plus P-4502E1 oxidized glycerol, 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 plus paraquat rates, suggesting synergistic interactions between paraquat and P-450. These results indicate that paraquat increases oxidation of glycerol to formaldehyde by microsomes and reconstituted systems, that H2O2 and iron play a role in the overall reaction, and that paraquat can substitute, in part, for P-450 in supporting oxidation of glycerol. However, cytochrome P-450 is required for elevated rates of formaldehyde production even in the presence of paraquat.
Clejan
L A
LA
Department of Biochemistry, Mount Sinai School of Medicine, New York, NY 10029.
Cederbaum
A I
AI
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D002712:Chlorides; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D019855:Ethylene Glycol; D005026:Ethylene Glycols / Q000378:metabolism; D005290:Ferric Compounds / Q000378:metabolism; D005557:Formaldehyde / Q000378:metabolism*; D005978:Glutathione / Q000494:pharmacology; D005990:Glycerol / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007501:Iron / Q000378:metabolism / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009249:NADP / Q000494:pharmacology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D010269:Paraquat / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000906:Antibodies; D000975:Antioxidants; D002712:Chlorides; D005026:Ethylene Glycols; D005290:Ferric Compounds; D005557:Formaldehyde; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase; D009251:NADPH-Ferrihemoprotein Reductase; D019855:Ethylene Glycol; D005978:Glutathione; D005990:Glycerol; D010269:Paraquat; C024555:ferric chloride