Lam E, Pande A, Callender R, Hilinski E F, Rentzepis P M, Packer L
Biochem Int. 1984 Feb;8(2):217-24.
Light-adapted purple membranes were modified with tetranitromethane by a new light-dependent procedure at pH 5.5 which results in a blue-shifted chromophore absorbing at 530nm. This modification affects two aromatic residues. The modified bacteriorhodopsin's ground state chromophore structure is probed by circular dichroism and resonance raman spectroscopy while its photocycle is studied by laser-flash photolysis in the picosecond, microsecond and millisecond time scale. After nitration, the main findings are 1) Interactions between neighboring chromophores are lost, 2) Modified bacteriorhodopsin contains a conformationally changed chromophore but retains a protonated Schiff's base as evidenced by a resonance raman band at 1652 cm-1, 3) A red-shifted intermediate is formed in less than 10 ps after laser excitation, 4) The decay of the M-intermediate is not significantly affected whereas the rise time of the intermediate is enhanced about two fold. These observations are relevant to the role of aromatic acid residues of the apoprotein in the determination of the chromophoric characteristics in bacteriorhodopsin.
通过一种新的光依赖程序，在pH 5.5条件下用四硝基甲烷对光适应的紫膜进行修饰，这会导致发色团蓝移并在530nm处吸收。这种修饰影响两个芳香族残基。通过圆二色性和共振拉曼光谱对修饰后的细菌视紫红质的基态发色团结构进行探测，同时在皮秒、微秒和毫秒时间尺度上通过激光闪光光解研究其光循环。硝化后，主要发现如下：1）相邻发色团之间的相互作用丧失；2）修饰后的细菌视紫红质含有构象改变的发色团，但保留了质子化的席夫碱，这由1652 cm-1处的共振拉曼带证明；3）激光激发后不到10皮秒形成一个红移中间体；4）M中间体的衰减没有受到显著影响，而中间体的上升时间增加了约两倍。这些观察结果与脱辅基蛋白的芳香酸残基在确定细菌视紫红质发色团特性中的作用有关。
