Rhodopsin photochemical transformations

Photochemical transformations of rhodopsin. The numbers in parentheses indicate the optical absorption maxima of the intermediates. The numbers in color on the right are approximate halftimes for the conversions in rod outer segment membranes near 37°... 

With the exception of photodissociation to radical ions observed for retinol in polar solvents (144), cis-trans isomerization is the major photochemical transformation undergone by all forms of the free retinyl-polyene chromophore. [Unidentified photochemical damage has been reported to occur with very low quantum yields, e.g., 0.04 in the case of all-trans retinal (177).] We shall subsequently see that critical comparisons between the photochemical behavior of the biopigments and that of the opsin-free chromophore have led to the conclusion that the protein moiety plays a major role in governing the photochemical mechanism in rhodopsin (176). It is, therefore, natural that in parallel to spectroscopic and theoretical investigations, considerable attention has been devoted to the photoisomerization of model compounds, particularly to that of retinal isomers. 

Kakitani, T., Matsuda, N., Hatano, Y, Shichida, Y, and Kakitani, H., Excited state dynamics of retinal proteins as studied by Fourier transform of optical absorption spectrum-II. Theoretical analysis of wavepacket propagation of rhodopsin, Photochem. Photobiol. 56, 989, 1992. 

The sequence of transformations in Figure 3 is believed to be involved in the photochemical cleavage of rhodopsin. ... 

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