Metmyoglobin/fluoride: Effect of distal histidine protonation on the association and dissociation rate constants
Metmyoglobin/fluoride: Effect of distal histidine protonation on the association and dissociation rate constants
复制标题
DOI：
10.1006/abbi.1998.0872
复制
发表时间：
1998-10-15
影响因子：
3.9
通讯作者：
Erman, JE
中科院分区：
文献类型：
--
作者：
Merryweather, J;Summers, F;Erman, JE
在 pH 3.4 至 11 之间研究了马高铁肌红蛋白/氟化物复合物的形成和解离动力学。在 pH 5 至 10 之间的积分 pH 值下测量了反应的离子强度依赖性。氢氟酸 HF 以 (4.7 +/- 0.7) x 10(4) M-1 s(-1) 的速率常数与高铁肌红蛋白结合。 pK(a) 为 4.4 +/- 0.5 的高铁肌红蛋白中的明显电离影响 HF 结合率，归因于远端组氨酸 His-64。 His-64 的质子化使 HF 结合率提高 2.6 倍。氟化物阴离子 F- 与高铁肌红蛋白结合的速率常数为 (5.6 +/- 1.4) x 10(-2) M-1 s(-1)，比 HF 慢约 10(6) 倍。无法检测到 HF 或 F- 与羟基高铁肌红蛋白的结合。远端组氨酸的质子化促进 HF 从高铁肌红蛋白/氟化物复合物中解离。 HF 解离速率常数为 1.9 +/- 0.3 s(-1)。氟阴离子的解离速度慢 2000 倍，速率常数为 (8.7 +/- 1.6) x 10(-4) s(-1)。荧光正肌红蛋白复合物中 His-64 电离的表观 pK(a) 为 5.7 +/- 0.1。缔合和解离速率常数相对独立于离子强度，二次动力学盐效应足以解释两者的离子强度变化，这与中性 HF 的缔合和解离主导氟化物与高铁肌红蛋白结合的动力学的观点一致。 (C) 1998 年学术出版社。
The kinetics of formation and dissociation of the horse metmyoglobin/fluoride complex has been investigated between pH 3.4 and 11. The ionic strength dependence of the reaction has been measured at integral pH values between pH 5 and 10. Hydrofluoric acid, HF, binds to metmyoglobin with a rate constant of (4.7 +/- 0.7) x 10(4) M-1 s(-1). An apparent ionization in metmyoglobin with a pK(a) of 4.4 +/- 0.5 influences the rate of HF binding and is attributed to the distal histidine, His-64. Protonation of His-64 increases the HF binding rate by a factor of 2.6. The fluoride anion, F-, binds to metmyoglobin with a rate constant of (5.6 +/- 1.4) x 10(-2) M-1 s(-1), about 10(6) times slower than HF. Binding of either HF or F- to hydroxymetmyoglobin cannot be detected. Protonation of the distal histidine facilitates HF dissociation from the metmyoglobin/fluoride complex. HF dissociates with a rate constant of 1.9 +/- 0.3 s(-1). The fluoride anion dissociates 2000 times more slowly, with a rate constant of (8.7 +/- 1.6) x 10(-4) s(-1). The apparent pK(a) for His-64 ionization in the fluorometmyoglobin complex is 5.7 +/- 0.1. The association and dissociation rate constants are relatively independent of ionic strength with secondary kinetic salt effects sufficient to account for the ionic strength variation of both, consistent with the idea that association and dissociation of neutral HF dominate the kinetics of fluoride binding to metmyoglobin. (C) 1998 Academic Press.