School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, UK.
School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, UK.
Nitric Oxide. 2018 Jan 30;72:16-23. doi: 10.1016/j.niox.2017.11.004. Epub 2017 Nov 8.
Globin-mediated nitric oxide (NO) dioxygenase and nitrite reductase activities have been proposed to serve protective functions within the cell by scavenging or generating NO respectively. Cytoglobin has rapid NO dioxygenase activity, similar to other globins, however, the apparent rates of nitrite reductase activity have been reported as slow or negligible. Here we report that the activity of cytoglobin nitrite reductase activity is strongly dependent on the oxidation state of the two surface-exposed cysteine residues. The formation of an intramolecular disulfide bond between cysteines C38 and C83 enhances the nitrite reductase activity by 50-fold over that of the monomer with free sulfhydryl or 140-fold over that of the dimer with intermolecular disulfide bonds. The NO dioxygenase reactivity of cytoglobin is very rapid with or without disulfide bond, however, binding of the distal histidine following dissociation of the nitrate are affected by the presence or absence of the disulfide bond. The nitrite reductase activity reported here for the monomer with intramolecular disulfide is much higher than of those previously reported for other mammalian globins, suggesting a plausible role for this biochemistry in controlling NO homeostasis the cell under oxidative and ischemic conditions.
球蛋白介导的一氧化氮 (NO) 双氧酶和亚硝酸盐还原酶活性被认为分别通过清除或生成 NO 来发挥细胞内的保护功能。细胞色素蛋白具有与其他球蛋白相似的快速 NO 双氧酶活性，然而，亚硝酸盐还原酶活性的表观速率已被报道为缓慢或可忽略不计。在这里，我们报告细胞色素蛋白亚硝酸盐还原酶活性强烈依赖于两个表面暴露的半胱氨酸残基的氧化状态。半胱氨酸 C38 和 C83 之间形成分子内二硫键，使亚硝酸盐还原酶活性比具有游离巯基的单体增强 50 倍，比具有分子间二硫键的二聚体增强 140 倍。无论是否形成二硫键，细胞色素蛋白的 NO 双氧酶反应性都非常迅速，然而，在硝酸盐解离后，远端组氨酸的结合受到二硫键存在与否的影响。这里报道的单体中二硫键的亚硝酸盐还原酶活性远高于以前报道的其他哺乳动物球蛋白，这表明这种生物化学在控制氧化和缺血条件下细胞内的 NO 动态平衡中可能发挥作用。
