Zavodnik I B, Lapshina E A
Institute of Biochemistry, Belarussian Academy of Sciences, Grodno, Belarus.
Biofizika. 2000 Sep-Oct;45(5):790-4.
It was shown that sodium dodecyl sulfate at concentrations not exceeding the critical micelle concentrations (0-1.9 mM) induced the conversion of oxy- and methemoglobin but not deoxyhemoglobin to hemichrome. The concentration dependences of hemichrome formation were represented as Hill plots, and the parameters of detergent binding were estimated. OxyHb in 20 mM potassium-phosphate buffer, pH 6.8, has two groups of binding sites: the first group is characterized by the Hill constant n1 = 2 and the concentration of half saturation [SDS]50 = 0.8 mM, and the second group is characterized by the Hill constant n2 = 8 and [SDS]50 = 0.9 mM. In the case of metHb one group of binding sites with the Hill constant n = 2 and half saturation concentration [SDS]50 = 0.2 mM was observed. An increase in environmental pH to 7.9 decreased the affinity of Hb for SDS. It is suggested that primary binding sites for SDS in oxyHb coincide with the anion-binding center of the Hb molecule. The interaction of the detergent with these binding sites induced a structural transition of the hemoprotein molecule. As a result of this transition, secondary binding sites were exposed. In a model system (hemin--imidazole in ethanol solution), the enthalpy of the transition of hemin from a high-spin to a low-spin state was estimated to be 47 +/- 7 kJ/mol.
结果表明，浓度不超过临界胶束浓度（0 - 1.9 mM）的十二烷基硫酸钠可诱导氧合血红蛋白和高铁血红蛋白转化为高铁血红素，但不能使脱氧血红蛋白发生转化。以希尔图表示高铁血红素形成的浓度依赖性，并估算去污剂结合参数。在pH 6.8的20 mM磷酸钾缓冲液中的氧合血红蛋白有两组结合位点：第一组的特征为希尔常数n1 = 2，半饱和浓度[SDS]50 = 0.8 mM；第二组的特征为希尔常数n2 = 8，[SDS]50 = 0.9 mM。对于高铁血红蛋白，观察到一组结合位点，其希尔常数n = 2，半饱和浓度[SDS]50 = 0.2 mM。环境pH增加到7.9会降低血红蛋白对SDS的亲和力。提示氧合血红蛋白中SDS的主要结合位点与血红蛋白分子的阴离子结合中心重合。去污剂与这些结合位点的相互作用诱导了血红蛋白分子的结构转变。这种转变导致二级结合位点暴露。在一个模型系统（乙醇溶液中的氯高铁血红素 - 咪唑）中，氯高铁血红素从高自旋态转变为低自旋态的焓估计为47±7 kJ/mol。
