Ultrafast isomerization dynamics of retinal in bacteriorhodopsin as revealed by femtosecond absorption spectroscopy

Carotenoid response to retinal excitation and photoisomerization dynamics in xanthorhodopsin

“…On the other hand, time constants extracted from SE kinetics of XR are 0.7 (70%) and 3.3 ps (30%), thus the overall decay is slower in XR. Based on number of previous reports, for global fitting of BR data in the visible region we fixed the components to 0.5 (excited-state lifetime) and 3 ps (J-K transition)[24]. The resulting fit provided amplitudes of these components of 92% and 8% at 477 nm (ESA region), respectively, matching the results obtained for decay of SE signal in near-IR.…”

“…Essentially the same result was obtained when the fast time constant was fixed to 0.7 ps obtained from fitting the near-IR kinetics of XR. We emphasize that no signal from J or K intermediates is present either in the region around 480 nm, or in the near-IR in BR[24], so the slower decay of the excited state in XR is not caused by product formation.…”

“…It must be noted, however, that fitting the SE kinetics of BR and XR revealed similar time constants. Time constants for SE of retinal in BR have been reported to be 0.5 ps (95%) and 2 ps (5%)[24], while values of 0.7 ps (64%) and 3.3 ps (36%) have been determined for XR[4]. Our single-wavelength fitting analysis showed corresponding time constants: 0.4 ps (91%) and 2.1 ps (9%) for BR; 0.7 (70%) and 3.3 ps (30%) for XR.…”

“…Thus, the slower overall excited-state decay in XR is almost solely due to increase of amplitude of the slower, ~3-ps component. The ~2-ps component has been attributed to a 13- cis , 15- syn retinal conformation in BR [24] and alternatively to conformational heterogeneity of retinal chromophore environment causing multicomponent decay of the excited state [30]. It is thus possible that either a fraction of the retinal chromophores with longer excited state lifetime in XR is larger than in BR, or that branching occurs in the excited state and a larger fraction evolves through a slower path.…”

Comparative Femtosecond Spectroscopy of Primary Photoreactions of Exiguobacterium sibiricum Rhodopsin and Halobacterium salinarum Bacteriorhodopsin

“…The formation of intermediate K 590 , which has a microsecond lifetime, completes the process of converting the energy of a light quantum into chemical energy in the form of conformational changes in the protein, which are subsequently used for proton transfer. In bR, an additional excited state decay in the picosecond timescale with a low amplitude was observed, which does not lead to retinal isomerization. ,,,,,,, …”