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 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. © 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:87–93, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21407