Cooperative cyanide dissociation from ferrous hemoglobin.
Cooperative cyanide dissociation from ferrous hemoglobin.
复制标题
亚铁血红蛋白协同氰化物解离。
DOI：
10.1016/s0021-9258(18)45871-1
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
A. Bellelli
中科院分区：
文献类型：
--
作者：
M. Brunori;G. Antonini;M. Castagnola;A. Bellelli
氰甲基血红蛋白(Hb+CN-)的快速还原会导致一种中间物种--亚铁血红蛋白的氰化物衍生物的形成，由于配体对亚铁血红素铁的亲和力极低，它会与未连接的血红蛋白解离。在CO存在和不存在的情况下，用人血红蛋白及其分离的α链和β链的瞬变光谱研究了中间体的性质。当与二亚硫酸盐混合时，血红素铁的还原和氰化物的解离的时间进程有相当大的重叠；加入氧化还原指示剂甲基紫精的反应混合物大大提高了还原速度，并允许明确地测定中间体的光谱和动力学性质。结果表明：(I)氰化物从分离的α链和β链(以及(αCO)2(β+CN-)2杂合体)上解离是一个简单的过程；(Ii)这两条链显示出相似的速率参数，但在Soret和可见光区域都显示出光谱不等价性；(Iii)协同效应被显示出来控制氰化物从血红蛋白中解离的速度，与氧的作用类似；(Iv)变构效应(典型的是六磷酸肌醇)通过稳定T态来增加总的解离速度。因此，我们首次证明了氰化物与亚铁血红蛋白的解离受季态控制，从而为分析血红蛋白的结构-功能关系增加了一种新的配体。
Rapid reduction of cyano-met hemoglobin (Hb+CN-) leads to the formation of an intermediate species, the cyanide derivative of ferrous hemoglobin, which dissociates to unliganded hemoglobin because of the extremely low affinity of the ligand for the ferrous heme iron. The properties of the intermediate were studied by transient spectroscopy in human hemoglobin and its isolated alpha and beta chains, in the presence and absence of CO. When mixing with dithionite, the time courses of reduction of the heme iron and dissociation of cyanide overlap considerably; addition to the reaction mixture of the redox indicator methyl viologen considerably increases the rate of reduction and allows unequivocal determination of the spectroscopic and kinetic properties of the intermediate. The results show that (i) the dissociation of cyanide from the isolated alpha and beta chains (as well as the (alpha CO)2(beta + CN-)2 hybrid) is a simple process; (ii) the two chains display similar rate parameters, but show spectroscopic inequivalence, both in the Soret and the visible regions; (iii) cooperative effects are shown to control the rate of dissociation of cyanide from hemoglobin, similarly to what happens for oxygen; and (iv) allosteric effectors (typically inositol hexaphosphate) increase the overall rate of dissociation by stabilization of the T state. We have, therefore, shown for the first time that the dissociation of cyanide from ferrous hemoglobin is controlled by the quaternary state, thereby adding one more ligand to the analysis of the structure-function relationships in hemoglobin.