Temperature and wavelength effects on the photochemistry of rhodopsin, isorhodopsin, bacteriorhodopsin and their photoproducts.

Abstract

THE primary photochemical event in visual pigments has become a matter of considerable controversy1–3. We recently reviewed the various models that have been proposed and argued that the accumulated evidence strongly favours the original suggestion of Kropf and Hubbard that the primary step involves a cis-trans isomerisation4. Evidence for isomerisation is based on the photoequilibrium that can be established, both at 77 K (ref. 5) and at room temperature6, between rhodopsin, bathorhodopsin (its primary photoproduct), and isorhodopsin (which contains a 9-cis chromophore). The equilibrium can be represented by This strongly suggests that the isomeric configuration of the chromophore of the common bathorhodopsin intermediate is all-trans retinal, and thus light has isomerised the chromophore from 11-cis to all-trans.