Bondar Ana-Nicoleta, Fischer Stefan, Suhai Sandor, Smith Jeremy C
J Phys Chem B. 2005 Aug 11;109(31):14786-8. doi: 10.1021/jp0531255.
Productive proton pumping by bacteriorhodopsin requires that, after the all-trans to 13-cis photoisomerization of the retinal chromophore, the photocycle proceeds with proton transfer and not with thermal back-isomerization. The question of how the protein controls these events in the active site is addressed here using quantum mechanical/molecular mechanical reaction-path calculations. The results indicate that, while retinal twisting significantly contributes to lowering the barrier for the thermal cis-trans back-isomerization, the rate-limiting barrier for this isomerization is still 5-6 kcal/mol larger than that for the first proton-transfer step. In this way, the retinal twisting is finely tuned so as to store energy to drive the subsequent photocycle while preventing wasteful back-isomerization.
细菌视紫红质产生质子泵作用要求，在视黄醛发色团从全反式光异构化为13-顺式后，光循环通过质子转移进行，而非热逆向异构化。本文利用量子力学/分子力学反应路径计算解决了蛋白质如何在活性位点控制这些事件的问题。结果表明，虽然视黄醛扭转对降低热顺反逆向异构化的势垒有显著贡献，但这种异构化的限速势垒仍比第一个质子转移步骤的势垒大5-6千卡/摩尔。通过这种方式，视黄醛扭转得到精细调节，以便储存能量来驱动后续的光循环，同时防止浪费的逆向异构化。
