Production of Nitric Oxide by Human Salivary Peroxidase and by Bovine Lactoperoxidase

Peroxidases catalyze the oxidation of nitrite to nitrate in the presence of hydrogen peroxide. Two pathways may occur: one entailing the intermediate formation of NO2 and the other implying the generation of peroxynitrite. The products of nitrite (NO2-) 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 NO2 and by HPLC to assess nitrates at the end of the reaction. Dialyzed saliva and LPO, in the presence of H2O2, convert nitrite into nitrate and form some NO, with a molar ratio of 10(3). In our experimental conditions, no NO2 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 NO2- into nitrate-forming small amounts of NO in the presence of H2O2 as an intermediate or a by-product, synthesized through the peroxynitrite pathway. (c) 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:87-93, 2012; View this article online at wileyonlinelibrary.com. DOI 10:1002/jbt.21407