title: Nitric oxide metabolism in mammalian cells: substrate and inhibitor profiles of a NADPH-cytochrome P450 oxidoreductase-coupled microsomal nitric oxide dioxygenase.
abstract: Human intestinal Caco-2 cells metabolize and detoxify NO via a dioxygen- and NADPH-dependent, cyanide- and CO-sensitive pathway that yields nitrate. Enzymes catalyzing NO dioxygenation fractionate with membranes and are enriched in microsomes. Microsomal NO metabolism shows apparent KM values for NO, O2, and NADPH of 0.3, 9, and 2 microM, respectively, values similar to those determined for intact or digitonin-permeabilized cells. Similar to cellular NO metabolism, microsomal NO metabolism is superoxide-independent and sensitive to heme-enzyme inhibitors including CO, cyanide, imidazoles, quercetin, and allicin-enriched garlic extract. Selective inhibitors of several cytochrome P450s and heme oxygenase fail to inhibit the activity, indicating limited roles for a subset of microsomal heme enzymes in NO metabolism. Diphenyleneiodonium and cytochrome c(III) inhibit NO metabolism, suggesting a role for the NADPH-cytochrome P450 oxidoreductase (CYPOR). Involvement of CYPOR is demonstrated by the specific inhibition of the NO metabolic activity by inhibitory anti-CYPOR IgG. In toto, the results suggest roles for a microsomal CYPOR-coupled and heme-dependent NO dioxygenase in NO metabolism, detoxification, and signal attenuation in mammalian cells.
authors.affiliation: Division of Critical Care Medicine, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, OH 45229, USA.
authors.forename: Craig K
authors.initials: CK
authors.lastname: Hallstrom
authors.forename: Anne M
authors.initials: AM
authors.lastname: Gardner
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gardner
mesh_terms: D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005609:Free Radicals; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D008956:Models, Chemical; D009251:NADPH-Ferrihemoprotein Reductase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D013997:Time Factors; D015032:Zinc / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D005609:Free Radicals; D006454:Hemoglobins; D007074:Immunoglobulin G; D013481:Superoxides; D009569:Nitric Oxide; D010105:Oxygenases; C114415:nitric oxide dioxygenase; D006419:Heme Oxygenase (Decyclizing); D009251:NADPH-Ferrihemoprotein Reductase; D015032:Zinc; D010100:Oxygen