Transmission of visual information in rod outer segments.

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Several steps of Photo-transduction process in rod outer segments were investigated by use of spectroscopic and biochemical techniques.1) Photochemical reaction of rhodopsin was investigated by means of picosecond laser photolysis. New bathochromic photoproduct "photorhodopsin", which was a precursor of bathorhodopsin, was found by excitation of rhodopsin with picosecond weak pulse. It was clarified that the reason why photorhodopsin was not detected in the preceding experiments was due to excitation of a rhodopsin sample with highly intense laser pulse.2) Deuterium effects on the formation and decay processes of photorhodopsin were investigated, where no deuterium effect was observed.3) Photo-isomerization of the chromophore of rhodopsin was investigated by use of low temperature spectrophotometry with retinal analogues. It was clarified that the isomerization of the retinylidene chromophore occured without any movement of its <beta> -ionone ring in the chromophore binding site of opsin and the conversion of bathorhodopsin to lumirhodopsin was induced by displacement of the <beta> -ionone ring.4) Photo-affinity labeling of <^3H> -cGMP against the rod outer segments showed that integral membrane proteins of molecular weights 100 K and 92 K were specifically labeled with cGMP. This result suggests that these proteins may be candidates of channel proteins in rod plasma membrane.5) cGMP-dependent phosphorylated proteins were purified from rod outer segments by column chromatography. Physiological role of the phosphorylation of the proteins was suggested to be intensification of activity of cGMP phosphodiesterase.6) Monoclonal antibodies of iodopsin and halorhodopsin were prepared.