Structure Formation Mechanism of Helix-Type Membrane Protein

对细菌视紫红质这一典型的膜蛋白进行了三种变性实验，以估计各种因素对膜蛋白结构形成的贡献。主要研究结果如下：1.通过加入醇而变性的细菌视紫红质。在醇变性过程中，三级结构被破坏，而二级结构保持完整。2.细菌视紫红质在纯己烷中不变性。然而，加入少量乙醇后，该结构被破坏，表明羟基是膜蛋白醇变性的原因。3.由变性动力学常数的温度依赖性估算了热变性的活化能。约40千卡/摩尔的活化能对应于膜中约10个氢键。Tihs数是跨膜螺旋之间可能的氢键的一半。因此，结构稳定性的机制是由于跨膜螺旋之间的极性相互作用，如氢键和离子对。

Three kinds of denaturation experiments were performed for a typical membrane protein, bacteriorhodopsin, in order to estimate the contribution of various factors to the structure formation of membrane proteins. The results were as follow : 1. Bacteriorhodopsin denatured by the addition of alcohols. In the alcohol denaturation, the tertiary structure was destroyed with the secondary structure remained intact. 2. Bacteriorhodopsin did not denature in pure hexane. However, the structure was destroyed by the addition of small amount of alcohol, indicating that the hydroxyl group is responsible for the alcohol denaturation of membrane proteins. 3. The activation energy of the thermal denaturation was estimated from the temperature dependence of the denaturation kinetic constant. The activation energy of about 40 kcal/mol corresponds to about ten hydrogen bonds in membrane. Tihs number is the half of possible hydrogen bonds between transmembrane helices. Consequently, the mechanism of the structural stability is due to the polar interactions such as hydrogen bonds and ion pairs between transmembrane helices.