Theory of the Optical Absorptions of Hypsorhodopsin and Bathorhodopsin

Abstract

In order to elucidate the observed absorption spectra of hypsorhodopsin and bathorhodopsin (being the first two intermediates in the photobleaching process of rhodopsin), the respective conformations of the chromophores of these intermediates are examined basing on our previous calculation on the optical absorption of PRSB (protonated retinal Schiff-base) with torsion about some single and double bonds in the polyene chain.
It is thus shown that the characteristic absorption spectrum of hypsorhodopsin can be explained by such a model for the chromophore that PRSB having largely twisted trans-form interacts with a negative point-charge e in the vicinity of N₁₆⁺. The conformation of PRSB with e in bathorhodopsin is also deduced to have a twisted trans-form with smaller torsion angles than those in the case of hypsorhodopsin.