Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
J Phys Chem B. 2009 Dec 17;113(50):16251-6. doi: 10.1021/jp9065289.
Proteorhodopsin (pR) is a membrane-embedded proton pump from the microbial rhodopsin family. Light absorption by its retinal chromophore initiates a photocycle, driven by trans/cis isomerization on the femtosecond to picosecond time scales. Here, we report a study on the photoisomerization dynamics of the retinal chromophore of pR, using dispersed ultrafast pump-dump-probe spectroscopy. The application of a pump pulse initiates the photocycle, and with an appropriately tuned dump pulse applied at a time delay after the dump, the molecules in the initial stages of the photochemical process can be de-excited and driven back to the ground state. In this way, we were able to resolve an intermediate on the electronic ground state that represents chromophores that are unsuccessful in isomerization. In particular, the fractions of molecules that undergo slow isomerization (20 ps) have a high probability to enter this state rather than the isomerized K-state. On the ground state reaction surface, return to the stable ground state conformation via a structural or vibrational relaxation occurs in 2-3 ps. Inclusion of this intermediate in the kinetic scheme led to more consistent spectra of the retinal-excited state, and to a more accurate estimation of the quantum yield of isomerization (Phi = 0.4 at pH 6).
紫膜质体（pR）是微生物视紫红质家族中的一种膜嵌入质子泵。其视黄醛发色团吸收光后，引发光循环，这一过程由飞秒到皮秒时间尺度内的顺/反异构驱动。在此，我们通过分散超快泵-泄-探测光谱法，对 pR 视黄醛发色团的光异构动力学进行了研究。泵浦脉冲的应用启动光循环，在泵浦后适当调谐的泄脉冲在延迟后应用，可以使光化学过程初始阶段的分子去激发并返回基态。通过这种方式，我们能够解析代表异构化不成功的发色团的电子基态中的中间态。特别是，经历慢异构化（20 ps）的分子分数很有可能进入这种状态，而不是异构化的 K 态。在基态反应表面，通过结构或振动弛豫返回稳定的基态构象需要 2-3 ps。将这种中间态纳入动力学方案导致视网膜激发态的光谱更一致，并更准确地估计异构化的量子产率（pH 值为 6 时为 0.4）。
