Picosecond events in the photochemical cycle of the light-driven chloride-pump halorhodopsin.

The early events in halorhodopsin after light excitation are studied with picosecond time resolution. Absorption and fluorescence measurements show that the electronically excited state of the incorporated retinal has a lifetime of 5 ps. Within that time a red-shifted photoproduct is formed that remains stable for at least 2 ns.