ИСТИНА

Visual pigment rhodopsin is one of the most well-studied representatives of retinal-binding proteins. It is typical member of the G-protein-coupled receptor family. Rhodopsin molecule consists of opsin protein and a chromophore, 11-cis retinal. 11-Cis-retinal covalently binds to the protein through a protonated Schiff base linkage to the ε-amino group of Lys296. Light quantum absorption leads to 11-cis retinal isomerisation to all-trans form. Photoisomerisation of retinal initiates conformational changes in the protein part of the rhodopsin molecule resulting in formation of intermediates with various lifetimes and spectral properties. Finally, rhodopsin phototransformation (photolysis) results in hydrolysis of Schiff base linkage and all-trans retinal release from the molecule. Elementary act of chromophore photoisomerisation in rhodopsin proceeds during time of about 80-100 fs with quantum yield of 0.65, resulting in formation of primary ground-state rhodopsin photoproduct by 200th fs, which then (~2 ps after) relaxes to bathorhodopsin. It is worth noting that in absorption kinetic curves of primary rhodopsin photoproduct oscillations provided by formation of coherent oscillation wave packets are observed. Ultrafast photochromic reversible reaction of visual pigment rhodopsin in the femtosecond range at room temperature is demonstrated. Femtosecond two pump-probe experiments with time resolution of 25 fs have been performed. The first рump pulse at 500 nm initiated cis-trans photoisomerisation of rhodopsin chromophore, 11-cis retinal, which resulted in formation of primary ground-state rhodopsin photoproduct within a mere 200 fs. The second pump pulse at 620 nm with varying delay of 200 to 3750 fs relative to the first рump pulse initiated the reverse phototransition of the primary photoproduct to rhodopsin. The results of this photoconversion have been observed on the differential spectra obtained after action of two pump pulses at the time delay of 100 ps relatively to first рump pulse. It was found that optical density decreased at 560 nm in the spectral region of bathorhodopsin absorption, and increased at 480 nm where rhodopsin absorbs. Rhodopsin photoswitching efficiency shows oscillation as a function of the time delay between the first рump pulse and the second рump pulse. Oscillations in transient absorption kinetics were documented by one pump-probe experiments with the excitation by 25 fs pulse at 500 nm. It was established that efficiency of the rhodopsin photoswitching and oscillations in transient absorption kinetics correlate well. The average quantum yield of reverse photoreaction initiated by the second pump pulse is estimated as 15  1 %. Molecular mechanisms of ultrafast photochrome reversible reaction of visual pigment rhodopsin may be used as a concept for development of ultrafast optical molecular switch.