Pande C, Callender R, Baribeau J, Boucher F, Pande A
Physics Department, City College of New York, New York.
Biochim Biophys Acta. 1989 Feb 28;973(2):257-62. doi: 10.1016/s0005-2728(89)80430-x.
Detergent solubilization and subsequent delipidation of bacteriorhodopsin (bR) results in the formation of a new species absorbing maximally at 480 nm (bR480). Upon lowering the pH, its absorption shifts to 540 nm (bR540). The pK of this equilibrium is 2.6, with the higher pH favoring bR480 (Baribeau, J. and Boucher, F. (1987) Biochim. Biophysica Acta, 890, 275-278). Resonance Raman spectroscopy shows that bR480, like the native bR, contains a protonated Schiff base (PSB) linkage between the chromophore and the protein. However, the Schiff base vibrational frequency in bR480, and its shift upon deuteration, are quite different from these in the native bR, suggesting changes in the Schiff base environment upon delipidation. Infrared absorption and circular-dichroism (CD) spectral studies do not show any net change in the protein secondary structure upon formation of bR480. It is shown that deprotonation of the Schiff base is not the only mechanism of producing hypsochromic shift in the absorption maximum of bR-derived pigments, subtle changes in the protein tertiary structure, affecting the Schiff base environment of the chromophore, may play an equally significant role in the color regulation of bR-derived pigments.
用去污剂溶解细菌视紫红质（bR）并随后进行脱脂处理，会形成一种在480 nm处有最大吸收峰的新物种（bR480）。降低pH值时，其吸收峰移至540 nm（bR540）。该平衡的pK值为2.6，较高的pH值有利于bR480的形成（巴里博，J.和布歇，F.（1987年）《生物化学与生物物理学报》，890，275 - 278）。共振拉曼光谱表明，bR480与天然bR一样，在发色团和蛋白质之间含有一个质子化席夫碱（PSB）键。然而，bR480中席夫碱的振动频率及其在氘化后的位移与天然bR中的有很大不同，这表明脱脂后席夫碱环境发生了变化。红外吸收和圆二色性（CD）光谱研究表明，形成bR480后蛋白质二级结构没有任何净变化。研究表明，席夫碱的去质子化不是导致bR衍生色素最大吸收峰发生蓝移的唯一机制，蛋白质三级结构的细微变化会影响发色团的席夫碱环境，这在bR衍生色素的颜色调节中可能同样起着重要作用。
