温度对菌紫质结构转变的影响

THERMAL EFFECT ON STRUCTURAL TRANSITION OF BACTERIORHODOPSIN

测量了不同温度下菌紫质的紫外—可见及红外吸收光谱,比较天然与变性菌紫质的吸附等温线。证明菌紫质在80℃前的可逆结构转变表现为结晶晶格协同效应降低,部分芳香族氨基酸显露,蛋白质构象的微小变化使视黄醛微环境改变。100℃引起的结构改变为不可逆,此时菌紫质三、四级结构解体,分子链展开并重聚,二级结构也发生变化,出现β结构,同时还保留部出α-螺旋,视黄醛全部游离。并就菌紫质的高热稳定性能做了讨论。

The UV-VIS and IR spectra of bacteriorhodopsin(BR) have been measured at different temperature. The isotherms of native and denatured BR have been compared. Below 80 ℃ the reversible structural transition is shown as reduction of cooperativity of crystalline lattice, partial exposure of hydropho-bic amino residues and a change of retinal's microenvironment induced by minor conformation shift of BR. At 100℃ the structural transition becomes irreversible. The tertiary and quarternary structure of BR are dissociated. Protein molecule is unfolded and aggregated. It has been demonstrated that the secondary structure of BR also changes significantly after thermal transition at 100℃. The β-structure emerges concomitantly with partly retained α-helix. The retinal chromophore is totally released at this temperature. It has been also discussed the possible reason for the high thermal stability of BR.