Primary processes in photochemistry of rhodopsin at room temperature

Abstract

MOST of the information concerning the primary photochemical events in vision has been derived from low temperature work^1–5. Recently, pulsed laser excitation methods with nanosecond^6–8 or picosecond⁹ time resolution have been applied, in an attempt at clarifying the primary act at physiological temperatures. These studies showed that prelumirhodopsin PLR; or bathorhodopsin), which is the primary photoproduct at 77 K, is also formed at room temperature, with a rise time of less than 6×10⁻¹²s (ref. 9) and a half life of ∼10⁻⁷s (refs 6–9). The problem remained, however, as to whether other primary transients, in addition to PLR, are formed at room temperature⁸. It is also important to establish if PLR is the unique precursor of the visual sequence at physiological temperatures, ruling out direct routes to subsequent intermediates—for example, lumirhodopsin (LR)—circumventing PLR. The present pulsed Nd laser study has attempted to clarify the above points, essentially testing the applicability of the low temperature photochemical picture (refs 10 and 11, and T.R., B. Honig, M.O. and T. Ebrey, unpublished) in physiological conditions.