Brittain T
J Inorg Biochem. 1981 Nov;15(3):243-52. doi: 10.1016/s0162-0134(00)80159-2.
The ferric hemes of valence hybrid hemoglobins combine with imidazole in a manner analogous with the hemes of methemoglobin. Equilibrium studies show that imidazole binding to methemoglobin is minimally described by the sum of two independent processes (k1 = 200 M-1 an K2 = 37 M-1), both of which contribute equally to the observed difference spectrum. Using valance hybrid hemoglobins, which show single binding processes under similar conditions, it is possible to identify the high affinity sites in methemoglobin with the alpha chains and the low affinity sites with the beta chains. Kinetic studies show that the valance hybrid hemoglobins react in a single exponential fashion with imidazole in contrast with methemoglobin which shows a biphasic reaction (k1 = 85 M-1 sec-1 k2 = 25 M-1 sec-1). A comparison of the rates of reaction of the hybrids allows the assignment of the fast phase in methemoglobin to the beta chains and the slow phase to the alpha chains. The heterogeneity of the imidazole reaction with methemoglobin occurs over the pH range 5.5-9.5 within which two ionization processes are discernable at pH 6.9 an 7.5.
价态杂合血红蛋白的三价铁血红素与咪唑结合的方式类似于高铁血红蛋白的血红素。平衡研究表明，咪唑与高铁血红蛋白的结合最少由两个独立过程的总和来描述（k1 = 200 M-1且K2 = 37 M-1），这两个过程对观察到的差光谱贡献相等。使用在相似条件下显示单一结合过程的价态杂合血红蛋白，可以确定高铁血红蛋白中与α链结合的高亲和力位点和与β链结合的低亲和力位点。动力学研究表明，与显示双相反应（k1 = 85 M-1秒-1，k2 = 25 M-1秒-1）的高铁血红蛋白不同，价态杂合血红蛋白与咪唑以单一指数方式反应。比较杂合体的反应速率可以将高铁血红蛋白中的快速相归为β链，慢速相归为α链。咪唑与高铁血红蛋白反应的异质性出现在pH范围5.5 - 9.5内，在该范围内，在pH 6.9和7.5时可辨别出两个电离过程。
