Studies on the reaction mechanism for reductive nitrosylation of ferrihemoproteins in buffer solutions
Studies on the reaction mechanism for reductive nitrosylation of ferrihemoproteins in buffer solutions
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DOI：
10.1021/ja953311w
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发表时间：
1996-06-19
影响因子：
15
通讯作者：
Ford, PC
中科院分区：
文献类型：
--
作者：
Hoshino, M;Maeda, M;Ford, PC
铁血红素蛋白在缓冲溶液中结合一氧化氮以产生它们的一氧化氮加合物。在pH值低于约2.5时，铁细胞色素c（Cyt（III））和高铁肌红蛋白（Mb（III））与NO的可逆结合被发现。7.0. Cyt（III）的平衡常数为（1.6 +/- 0.1）x 10（4）M（-1），Mb（III）的平衡常数为（1.3 +/- 0.1）x 10（4）M（-1）。在较高pH下，不再观察到NO加合物的可逆形成; Cyt（III）的NO加合物（Cyt（III）-NO）经历还原为亚铁细胞色素c，Cyt（II），Mb（III）的NO加合物（Mb（III）-NO）经历还原为Mb（II）的亚硝酰基加合物（Mb（II）-NO）。高铁血红蛋白（Hb（III））即使在pH < 6时也容易与NO反应，生成血红蛋白的亚硝酰加合物（Hb（II）-NO）。测定Cyt（II）、Mb（II）-NO和Hb（II）-NO的形成速率作为NO和OH-浓度的函数。动力学分析表明，Cyt（III）-NO和Mb（III）-NO在较高pH值下分别被OH-亲核进攻生成Cyt（II）和Mb（II）.如此产生的Mb（II）进一步与NO反应，得到Mb（II）-NO。对于Hb（III），在过量NO存在下，亚硝酰加合物（Hb（III）-NO）可与OH-和H2O反应生成Hb（II）-NO。亚硝酰高铁血红素蛋白与OH-反应的速率常数为Cyt（III）-NO为（1.5 +/- 0.1）x 10（3）M（-1）s（-1），Mb（III）-NO为（3.2 +/- 0.2）x 10（2）M（-1）s（-1），和（3.2 +/- 0.2）x 10（3）M（-1）s（-1）对于Hb（III）-NO。在pH < 6.0时观察到的Hb（III）的还原性亚硝基化通过H2O与Hb（III）-NO的反应来解释：速率常数为（1.1 +/-0.1）× 10（-3）s（-1）。
Ferrihemoproteins in buffer solutions bind nitric oxide to yield their nitric oxide adducts. Reversible binding of NO was found for ferricytochrome c (Cyt(III)) and metmyoglobin (Mb(III)) at pH values lower than ca. 7.0. The equilibrium constants were obtained as (1.6 +/- 0.1) x 10(4) M(-1) for Cyt(III) and (1.3 +/- 0.1) x 10(4) M(-1) for Mb(III). At higher pH, the reversible formation of the NO adducts is no longer observed; the NO adduct of Cyt(III) (Cyt(III)-NO) undergoes reduction to ferrocytochrome c, Cyt(II), and that of Mb(III) (Mb(III)-NO) to the nitrosyl adduct of Mb(II) (Mb(II)-NO). Methemoglobin (Hb(III)) reacts readily with NO even at pH < 6 to give the nitrosyl adduct of hemoglobin (Hb(II)-NO). The rates for the formation of Cyt(II), Mb(II)-NO, and Hb(II)-NO were measured as functions of NO and OH- concentrations. Kinetic analysis indicates that Cyt(III)-NO and Mb(III)-NO undergo nucleophilic attack by OH- at higher pH to yield Cyt(II) and Mb(II), respectively. Mb(II) thus produced further reacts with NO to give Mb(II)-NO. For Hb(III), the nitrosyl adduct (Hb(III)-NO) was found to react with both OH- and H2O to give Hb(II)-NO in the presence of excess NO. The rate constants for the reaction between the nitrosyl ferrihemoproteins and OH- were determined as (1.5 +/- 0.1) x 10(3) M(-1) s(-1) for Cyt(III)-NO, (3.2 +/- 0.2) x 10(2) M(-1) s(-1) for Mb(III)-NO, and (3.2 +/- 0.2) x 10(3) M(-1) s(-1) for Hb(III)-NO. The reductive nitrosylation of Hb(III) observed at pH < 6.0 is explained by reaction of H2O with Hb(III)-NO: the rate constant is (1.1 +/- 0.1) x 10(-3) s(-1).