Formation of photorhodopsin, a precursor of bathorhodopsin, detected by picosecond laser photolysis at room temperature

The primary photochemical reaction of rhodopsin was investigated by means of picosecond laser photolysis at room temperature. Transient absorption spectra of intermediates of rhodopsin were measured, together with kinetic measurements of absorbance at selected wavelengths, in the picosecond time region, following excitation with a 532 nm picosecond laser pulse (duration 25 ps). A bathochromic photoproduct, a precursor of bathorhodopsin, was found. We called this product ‘photorhodopsin’. The absorption spectrum lay at a slightly longer wavelength than that of bathorhodopsin. Photorhodopsin was produced within the 25 ps pulse duration and decayed to bathorhodopsin, with a time constant of about 40 ps in the case of cattle rhodopsin system and of several hundreds of ps in the case of squid and octopus rhodopsin systems.