title: Production of nitric oxide by human salivary peroxidase and by bovine lactoperoxidase.
abstract: Peroxidases catalyze the oxidation of nitrite to nitrate in the presence of hydrogen peroxide. Two pathways may occur: one entailing the intermediate formation of NO(2) and the other implying the generation of peroxynitrite. The products of nitrite (NO(2) (-) ) oxidation by salivary peroxidase (SPO) and commercial bovine lactoperoxidase (LPO) are studied by utilizing an electrochemical assay that allows the direct, continuous monitoring of NO and/or NO(2) and by HPLC to assess nitrates at the end of the reaction. Dialyzed saliva and LPO, in the presence of H(2) O(2) , convert nitrite into nitrate and form some NO, with a molar ratio of 10(3) . In our experimental conditions, no NO(2) was detectable among the products of nitrite oxidation. SCN(-) inhibits NO formation and so does I(-) , although at higher concentrations. No effects are observed with Cl(-) or Br(-) . We conclude that SPO and LPO transform NO(2) (-) into nitrate-forming small amounts of NO in the presence of H(2) O(2) as an intermediate or a by-product, synthesized through the peroxynitrite pathway.
authors.affiliation: Department of Internal Medicine, Laboratory of Biochemistry, The University of Perugia, Via del Giochetto, I-06122, Perugia, Italy. crlpal@unipg.it
authors.forename: Carlo Alberto
authors.initials: CA
authors.lastname: Palmerini
authors.forename: Fabio
authors.initials: F
authors.lastname: Marmottini
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Arienti
mesh_terms: D000818:Animals; D002417:Cattle; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007454:Iodides / Q000737:chemistry; D007784:Lactoperoxidase / Q000037:antagonists & inhibitors / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D009569:Nitric Oxide / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry; D009585:Nitrogen Dioxide / Q000737:chemistry; D009195:Peroxidase / Q000037:antagonists & inhibitors / Q000737:chemistry*; D012463:Saliva / Q000201:enzymology*; D012966:Sodium Cyanide / Q000737:chemistry
chemical_list: D007454:Iodides; D009566:Nitrates; D009573:Nitrites; D009569:Nitric Oxide; D006861:Hydrogen Peroxide; D007784:Lactoperoxidase; D009195:Peroxidase; D012966:Sodium Cyanide; D009585:Nitrogen Dioxide