Lau P W, Asakura T
J Biol Chem. 1979 Apr 25;254(8):2595-9.
A spin label attached to a propionic acid group of the heme has been used to probe the heme environment of the alpha and beta chains of hemoglobin in both the subunit and tetrameric forms. The electron paramagnetic resonance (EPR) studies of hemoglobin hybrids in which the spin label is attached to either the alpha- or beta-heme (alpha2SLbeta 2 or alpha2beta2SL) and spin-labeled isolated chains (alphaSL and betaSL) show that: 1) alpha- and beta-hemes have different environments in the tetrameric forms of oxy-, deoxy-, and methemoglobins as well as in isolated single chains; 2) when isolated subunits associate to form hemoglobin tetramers, the environment of the alpha-heme changes more drastically than that of the beta-heme; 3) upon deoxygenation of hemoglobin, the structure in the vicinity of the alpha-heme changes more drastically than that of the beta-heme; and 4) upon the addition of organic phosphates to methemoglobin, the change in the spin state of the heme irons mainly arises from beta-heme. The results demonstrate conclusively that the alpha and the beta subunits of hemoglobin are structurally nonequivalent as are their structural changes as the result of ligation. The relationship of EPR spectrum and structure of hemoglobin is discussed.
一个连接到血红素丙酸基团上的自旋标记已被用于探测血红蛋白α链和β链在亚基形式和四聚体形式下的血红素环境。对自旋标记连接到α-血红素或β-血红素上的血红蛋白杂合体（α2SLβ2或α2β2SL）以及自旋标记的分离链（αSL和βSL）进行的电子顺磁共振（EPR）研究表明：1）在氧合血红蛋白、脱氧血红蛋白和高铁血红蛋白的四聚体形式以及分离的单链中，α-血红素和β-血红素具有不同的环境；2）当分离的亚基缔合形成血红蛋白四聚体时，α-血红素的环境变化比β-血红素的变化更为剧烈；3）血红蛋白脱氧时，α-血红素附近的结构变化比β-血红素的变化更为剧烈；4）向高铁血红蛋白中添加有机磷酸盐时，血红素铁自旋状态的变化主要源于β-血红素。结果确凿地证明，血红蛋白的α亚基和β亚基在结构上是不等同的，它们因配体结合而发生的结构变化也是如此。文中讨论了EPR光谱与血红蛋白结构的关系。
