Moulton D P, McDonald M J
Department of Chemistry, College of Arts and Sciences, University of Massachusetts at Lowell 01854.
Biochem Biophys Res Commun. 1994 Mar 30;199(3):1278-83. doi: 10.1006/bbrc.1994.1369.
Heme chain exchange was employed to investigate the dimer dissociation reaction of human apohemoglobin in 0.1 M potassium phosphate buffer, pH 7.0, at 20 degrees C. Incubation of apohemoglobin (alpha 0 beta 0) with either alpha h (or beta h) allowed the monitoring of the formation of a semihemoglobin alpha h beta 0 (or alpha 0 beta h) species with time. Analysis revealed that the rate of formation of both semihemoglobins was essentially identical and coincided with the disappearance of heme chain. Time courses were exponential and followed first order kinetics yielding a dimer dissociation rate constant of 0.54 (+/- 0.07) h-1. A study over the pH range from 6.5 to 8.0 revealed that this dissociation rate exhibited a maximum at pH 7.0 (implicating a histidyl residue). The effect of temperature (6-37 degrees C) on this dimer dissociation rate yielded a linear Arrhenius Plot and an energy of activation of 7.2 kcal/mol. These results are consistent with alpha G-beta G helical pairing being a major contributor to apohemoglobin dimer integrity.
采用血红素链交换法研究了人脱辅基血红蛋白在0.1 M磷酸钾缓冲液（pH 7.0，20℃）中的二聚体解离反应。将脱辅基血红蛋白（α0β0）与αh（或βh）一起孵育，可监测半血红蛋白αhβ0（或α0βh）物种随时间的形成情况。分析表明，两种半血红蛋白的形成速率基本相同，且与血红素链的消失一致。时间进程呈指数形式，遵循一级动力学，二聚体解离速率常数为0.54（±0.07）h-1。在pH 6.5至8.0范围内的研究表明，这种解离速率在pH 7.0时达到最大值（表明存在一个组氨酸残基）。温度（6-37℃）对该二聚体解离速率的影响产生了线性阿伦尼乌斯图，活化能为7.2 kcal/mol。这些结果与αG-βG螺旋配对是脱辅基血红蛋白二聚体完整性的主要贡献因素一致。
