FLASH PHOTOLYSIS OF ROD PARTICLE SUSPENSIONS

Abstract. Flash photolytic experiments with suspensions of rod particles isolated from cattle eyes reveal that at low temperatures a transient is formed following irradiation which preceeds lumirhodopsin in the bleaching process. Kinetic studies, in the range -75°C to -50°C, suggest that the transient is composed of three intermediate species, having similar absorption spectra but changing to lumirhodopsin at different rates. The energies of activation of the decay reactions appear to be identical and equal 12.5°3 kcal/mole. Spectrophotometric experiments have demonstrated that the low temperature transient is stable at liquid nitrogen temperatures and suggest that it can be reversibly converted to a mixture of rhodopsin and isorhodopsin at -195°C.
A detailed comparison of light initiated reactions of rhodopsin in rod particle suspensions and in solutions reveals striking similarity in the two systems.