Myoglobin (Mb), generally taken as the molecular model of monomeric globular heme-proteins, is devoted: (i) to act as an intracellular oxygen reservoir, (ii) to transport oxygen from the sarcolemma to the mitochondria of vertebrate heart and red muscle cells, and (iii) to act as a scavenger of nitrogen and oxygen reactive species protecting mitochondrial respiration. Here, the first evidence of ^·NO inhibition of ferric Mb- (Mb(III)) mediated detoxification of peroxynitrite is reported, at pH 7.2 and 20.0 °C. ^·NO binds to Mb(III) with a simple equilibrium; the value of the second-order rate constant for Mb(III) nitrosylation (i.e., ^·NOk_on) is (6.8 ± 0.7) × 10⁴ M⁻¹ s⁻¹ and the value of the first-order rate constant for Mb(III)-NO denitrosylation (i.e., ^·NOk_off) is 3.1 ± 0.3 s⁻¹. The calculated value of the dissociation equilibrium constant for Mb(III)-NO complex formation (i.e., ^·NOk_off/^·NOk_on = (4.6 ± 0.7) × 10⁻⁵ M) is virtually the same as that directly measured (i.e., ^·NOK = (3.8 ± 0.5) × 10⁻⁵ M). In the absence of ^·NO, Mb(III) catalyzes the conversion of peroxynitrite to NO₃⁻, the value of the second-order rate constant (i.e., ^Pk_on) being (1.9 ± 0.2) × 10⁴ M⁻¹ s⁻¹. However, in the presence of ^·NO, Mb(III)-mediated detoxification of peroxynitrite is only partially inhibited, underlying the possibility that also Mb(III)-NO is able to catalyze the peroxynitrite isomerization, though with a reduced rate (^Pk_on* = (2.8 ± 0.3) × 10³ M⁻¹ s⁻¹). These data expand the multiple roles of ^·NO in modulating heme-protein actions, envisaging a delicate balancing between peroxynitrite and ^·NO, which is modulated through the relative amount of Mb(III) and Mb(III)-NO.

Graphic abstract

中文翻译：

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亚硝酸铁化的肌红蛋白可催化过亚硝酸盐清除。

肌红蛋白（Mb）通常被认为是单体球状血红蛋白的分子模型，其作用是：（i）充当细胞内的氧气储库，（ii）将氧气从肌膜运输到脊椎动物心脏和红色肌肉的线粒体（iii）充当保护线粒体呼吸的氮和氧反应物种的清除剂。这里，第一个证据^· NO抑制铁MB-的（MB（III））过氧亚硝酸盐介导的解毒报道，在pH 7.2和20.0℃。^· NO以简单的平衡与Mb（III）结合；Mb（III）亚硝基化的二阶速率常数（即^·NO k _on）的值为（6.8±0.7）×10 ⁴  M ^-1  s ^-1和一级速率常数为MB（III）-NO denitrosylation（即的值。，^·NO ķ_断）为3.1±0.3秒^-1。解离平衡常数为MB（III）的计算值-NO复合物形成（即，^·NO ķ_关闭/ ^·NO ķ_上 =（4.6±0.7）×10 ^-5 作为直接测量M）几乎是相同的（即^·NO K  ＝（3.8±0.5）×10 ^-5  M）。在没有^· NO，MB（III）催化过氧到NO的转化₃ ^- ，二阶速率常数的值（即。，（^P k _on）为（1.9±0.2）×10 ⁴  M ^-1  s ^-1。然而，在存在^· NO，MB（III）过氧亚硝酸盐介导的解毒仅部分地抑制，底层的可能性也MB（III）-NO是能够催化过氧化亚硝酸盐异构化，尽管以减小的速率（^P ķ_开* =（2.8±0.3）×10 ³  M ^-1  s ^-1）。这些数据展开的多重角色^· NO在调节血红素蛋白的行动，设想之间过氧化亚硝酸盐和微妙的平衡^？NO，其通过Mb（III）和Mb（III）-NO的相对量进行调节。

图形摘要