PICOSECOND LASER PHOTOLYSIS OF SQUID RHODOPSIN AT ROOM AND LOW TEMPERATURES

Abstract

Abstract. Squid rhodopsin extracted with 2% digitonin (pH 10.5 or 7.0) was excited with a 347 nm light pulse from a mode‐locked ruby laser at room temperature. Within 19 ps after the excitation, absorbance at 430 nm due to hypsorhodopsin increased and subsequently decreased with a decay time of 45 ± 10 ps. Absorbance at 550 nm due to bathorhodopsin increased with a rise time of 50 ± 10 ps. These results are the first observations of hypsorhodopsin at room temperature and clearly show that hypsorhodopsin is a precursor of bathorhodopsin which has been considered to be the earliest photoproduct in the photobleaching process of rhodopsin. Hypsorhodopsin appeared with a rise time of 70 ± 10 ps at 421 nm at liquid nitrogen temperature without any bathorhodopsin being observed during the formation of hypsorhodopsin. An experiment using an N 2 laser showed that squid bathorhodopsin converted to lumirhodopsin with a decay time of about 300 ns at room temperature.