The cycle of photochromic reactions of a bacteriorhodopsin analog with 4-keto-retinal

Photochemical reactions in a bacteriorhodopsin analog with 4-keto-retinal (4-keto-BR) were studied by using low-temperature and pulsed laser absorption spectroscopy. A photocycle of the photochemical reactions of 4-keto-BR is proposed, which, unlike the photocycle of native BR, includes several spectrally and kinetically distinguishable M-type and O-type intermediates.