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Oxidation of Nitric Oxide in Aqueous Solution to Nitrite but not Nitrate: Comparison with Enzymatically Formed Nitric Oxide From L-Arginine
Louis J. Ignarro, Jon M. Fukuto, Jeannete M. Griscavage, Norma E. Rogers and Russell E. Byrns
Proceedings of the National Academy of Sciences of the United States of America
Vol. 90, No. 17 (Sep. 1, 1993), pp. 8103-8107
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2362973
Page Count: 5
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Nitric oxide (NO) in oxygen-containing aqueous solution has a short half-life that is often attributed to a rapid oxidation to both NO- 2 and NO- 3. The chemical fate of NO in aqueous solution is often assumed to be the same as that in air, where NO is oxidized to NO2 followed by dimerization to N2O4. Water then reacts with N2O4 to form both NO- 2 and NO- 3. We report here that NO in aqueous solution containing oxygen is oxidized primarily to NO- 2 with little or no formation of NO- 3. In the presence of oxyhemoglobin or oxymyoglobin, however, NO and NO- 2 were oxidized completely to NO- 3. Methemoglobin was inactive in this regard. The unpurified cytosolic fraction from rat cerebellum, which contains constitutive NO synthase activity, catalyzed the conversion of L-arginine primarily to NO- 3 (NO- 2/NO- 3 ratio = 0.25). After chromatography on DEAE-Sephacel or affinity chromatography using 2',5'-ADP-Sepharose 4B, active fractions containing NO synthase activity catalyzed the conversion of L-arginine primarily to NO- 2 (NO- 2/NO- 3 ratio = 5.6) or only to NO- 2, respectively. Unpurified cytosol from activated rat alveolar macrophages catalyzed the conversion of L-arginine to NO- 2 without formation of NO- 3. Addition of 30 μM oxyhemoglobin to all enzyme reaction mixtures resulted in the formation primarily of NO- 3 (NO- 2/NO- 3 ratio = 0.09 to 0.20). Cyanide ion, which displaces NO- 2 from its binding sites on oxyhemoglobin, inhibited the formation of NO- 3, thereby allowing NO- 2 to accumulate. These observations indicate clearly that the primary decomposition product of NO in aerobic aqueous solution is NO- 2 and that further oxidation to NO- 3 requires the presence of additional oxidizing species such as oxyhemoproteins.
Proceedings of the National Academy of Sciences of the United States of America © 1993 National Academy of Sciences