Femtosecond Spectroscopy of Halorhodopsin and Rhodopsin in a Broad Spectral Range of 400−1000 nm

Abstract

Femtosecond pump−probe spectroscopy of halorhodopsin from Halobacterium halobium and rhodopsin from octopus (paroctopus defleini) has been studied in a wide spectral range extending from 400 to 1000 nm. There are five common features to halorhodopsin and rhodopsin in the transient absorption and gain spectra. A comparative description of the primary photochemistries in the retinal proteins including bacteriorhodopsin is presented to explain the present experimental results systematically together with the previous studies. In the model there is a branching from the Franck−Condon state into coherent and incoherent channels. The former is the rapid process of direct formation of the first intermediate (bathorhodopsin for rhodopsin and hRK intermediate for halorhodopsin), and the latter is the thermalization of the excited state in the retinoid proteins, from which slow formation of the first intermediate takes place.