title: Human recombinant cytochrome P450 enzymes display distinct hydrogen peroxide generating activities during substrate independent NADPH oxidase reactions.
abstract: Microsomal enzymes generate H2O2 in the presence of NADPH. In this reaction, referred to as "oxidase" activity, H2O2 is generated directly or indirectly via the formation of superoxide anion. In the presence of redox active transition metals, H2O2 can form highly toxic hydroxyl radicals and, depending on the "oxidase" activity of individual cytochrome P450 isoenzymes, this can compromise cellular functioning and contribute to tissue injury. In the present studies, we compared the initial rates of H2O2 generating activity of microsomal preparations containing various human recombinant cytochromes P450s. In the absence of cytochrome P450s the human recombinant NADPH cytochrome P450 reductase (CPR) generated low, but detectable amounts of H2O2 (∼0.04 nmol H2O2/min/100 units of reductase). Significantly greater activity was detected in preparations containing individual cytochrome P450s coexpressed with CPR (from 6.0 nmol H2O2/min/nmol P450 to 0.2 nmol/min/nmol P450); CYP1A1 was the most active, followed by CYP2D6, CYP3A4, CYP2E1, CYP4A11, CYP1A2, and CYP2C subfamily enzymes. H2O2 generating activity of the cytochrome P450s was independent of the ratio of CYP/CPR. Thus, similar H2O2 generating activity was noted with the same cytochrome P450s (CYP3A4, CYP2E1, and CYP2C9) expressed at or near the ratio of CYP/CPR in human liver microsomes (5-7), and when CPR was present in excess (CYP/CPR = 0.2-0.3). Because CYP3A4/5/7 represent up to 40% of total cytochrome P450 in the liver, these data indicate that these enzymes are the major source of H2O2 in human liver microsomes.
authors: Department of Pharmacology and Toxicology, Rutgers University, Piscataway, New Jersey 08854.
authors: Vladimir
authors: V
authors: Mishin
authors: Department of Environmental Health Science, School of Health Sciences and Practice, New York Medical College, Valhalla, New York 10595.
authors: Diane E
authors: DE
authors: Heck
authors: Department of Pharmacology and Toxicology, Rutgers University, Piscataway, New Jersey 08854.
authors: Debra L
authors: DL
authors: Laskin
authors: Department of Environmental and Occupational Medicine, Rutgers University-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854 jlaskin@eohsi.rutgers.edu.
authors: Jeffrey D
authors: JD
authors: Laskin
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007527:Isoenzymes; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D006861:Hydrogen Peroxide; D009251:NADPH-Ferrihemoprotein Reductase
keywords: cytochrome P450; cytochrome P450 reductase; microsomes; reactive oxygen species; “oxidase” reaction