Sibmooh Nathawut, Piknova Barbora, Rizzatti Fabiola, Schechter Alan N
Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Biochemistry. 2008 Mar 4;47(9):2989-96. doi: 10.1021/bi702158d. Epub 2008 Jan 29.
The reaction of deoxyhemoglobin with nitric oxide (NO) or nitrite ions (NO 2 (-)) produces iron-nitrosyl-hemoglobin (HbNO) in contrast to the reaction with oxyhemoglobin, which produces methemoglobin and nitrate (NO 3 (-)). HbNO has not been associated with the known bioactivities of NO. We hypothesized that HbNO in erythrocytes could be an important source of bioactive NO/nitrite if its oxidation was coupled to the ascorbic acid (ASC) cycle. Studied by absorption and electron paramagnetic resonance (EPR) spectroscopy, DHA oxidized HbNO to methemoglobin and liberated NO from HbNO as determined by chemiluminescence. Both DHA and ascorbate free radical (AFR), the intermediate between ASC and DHA, enhanced NO oxidation to nitrite, but not nitrate; nor did either oxidize nitrite to nitrate. DHA increased the basal levels of nitrite in erythrocytes, while the reactions of nitrite with hemoglobin are slow. In erythrocytes loaded with HbNO, HbNO disappeared after DHA addition, and the AFR signal was detected by EPR. We suggest that the ASC-AFR-DHA cycle may be coupled to that of HbNO-nitrite and provide a mechanism for the endocrine transport of NO via hemoglobin within erythrocytes, resulting in the production of intracellular nitrite. Additionally, intracellular nitrite and nitrate seem to be largely generated by independent pathways within the erythrocyte. These data provide a physiologically robust mechanism for erythrocytic transport of NO bioactivity allowing for hormone-like properties.
与氧合血红蛋白反应生成高铁血红蛋白和硝酸盐（NO₃⁻）不同，脱氧血红蛋白与一氧化氮（NO）或亚硝酸根离子（NO₂⁻）反应生成铁亚硝酰血红蛋白（HbNO）。HbNO与已知的NO生物活性无关。我们推测，如果红细胞中的HbNO氧化与抗坏血酸（ASC）循环相耦合，那么它可能是生物活性NO/亚硝酸盐的重要来源。通过吸收光谱和电子顺磁共振（EPR）光谱研究发现，DHA将HbNO氧化为高铁血红蛋白，并通过化学发光法测定从HbNO中释放出NO。DHA和抗坏血酸自由基（AFR，ASC和DHA之间的中间体）均增强了NO氧化为亚硝酸盐的过程，但不包括氧化为硝酸盐；二者也都没有将亚硝酸盐氧化为硝酸盐。DHA增加了红细胞中亚硝酸盐的基础水平，而亚硝酸盐与血红蛋白的反应较慢。在加载了HbNO的红细胞中，添加DHA后HbNO消失，并且通过EPR检测到AFR信号。我们认为，ASC-AFR-DHA循环可能与HbNO-亚硝酸盐循环相耦合，并为红细胞内通过血红蛋白进行NO的内分泌转运提供了一种机制，从而导致细胞内亚硝酸盐的产生。此外，细胞内亚硝酸盐和硝酸盐似乎很大程度上是由红细胞内独立的途径产生的。这些数据为红细胞运输NO生物活性提供了一种生理上强大的机制，使其具有类似激素的特性。
