[Photo-induced processes and reaction dynamics in bacteriorhodopsin].

In this review we have focused on the advances madein observing the photo-induced response in bacteriorhodopsin and understanding the mechanisms of retinal-protein interactions which are still obscure. We discuss our recent data obtained on the wild type of bacteriorhodopsin and model compounds. This paper presents our new spectroscopic data on amino acids obtained using FT-IR emission spectroscopy. Based on the characteristics of the structure and optical properties of glycine and L-lysine that simulate a photo-induced behaviour of an opsin under natural conditions we tried to find an answer to one of the most important questions concerning the role of protein in the primary processes in bacteriorhodopsin.

FTIR emission spectra of bacteriorhodopsin in a vibrational excited state.

Vibrational IR-emission spectra of bacteriorhodopsin (bR) were recorded under continuous illumination with visible light at room temperature. They contain selective information about the chromophore, Schiff base, and opsin. The spectral bands were identified by comparing the data with resonance Raman and IR absorption data. The IR-emission spectra were shown to contain a set of bands characteristic for both all-trans (bR568) and 13-cis conformations (K610-like intermediate) simultaneously. Variation of spectral composition and the intensity of visible light illumination influenced the spectral traces and intensity distribution between them. Greater intensity of deformational vibrations suggests distorted retinal structure in the vibrationally excited ground electronic state. The origin of the emitting species of bR is discussed.

[Absorption of infrared radiation by a thin water layer]. / Pogloshchenie IK-izlucheniia tonkim sloem vody.

The unhomogeneous distribution of infrared absorption in a thin water layer and its time instability were explained. The parameters of interribbon interaction in the case of thin water layers with bound influence were evaluated.

[Investigation of the effects of dehydration on bacterial rhodopsin by laser resonance Raman spectroscopy]. / Issledovanie vliianiia degidratatsii na bakterial'nyi rodopsin metodom rezonansnoi spektroskopii kombinatsionnogo rasseianiia sveta.

Using laser resonance Raman spectroscopy the influence of water on the structure of the chromophore centre in bacteriorhodopsin from Halobacterium halobium has been studied. The absorption band has been found to shift from 568 nm to 506 nm due to local protein changes in the chromophore centre near Schiff base bounding retinal with the lysine residue. These changes are not accompanied by the Schiff base deprotonation. Dehydration decreases essentially the reaction rate of the cis in equilibrium trans isomerization processes. In the dry state the potential barriers of the cis in equilibrium trans transition reaction turns out to be higher than that of the reverse reaction. As a result the equilibrium shifts to the cis-retinal form. Comparison of the Raman spectra of the M412 intermediate in wet and dry states of purple membranes leads to the conclusion that in water suspensions of purple membranes the chromophore state of the M412 intermediate is closer to cis- than to trans-retinal.

Effect of water on the structure of bacteriorhodopsin and photochemical processes in purple membranes.

Visible and infrared spectra of bacteriorhodopsin films under different humidities at room and low temperatures are investigated. On dehydration of purple membranes at room temperatures an additional chromophore state with the absorption band at 506 nm is revealed. The photocycle of purple membranes in the dry state is devoid of the 550 nm intermediate and involves the long-lived intermediate at 412 nm. As water is removed, the 550 nm intermediate becomes undetectable. The analysis of the infrared spectra shows that dehydration does not affect the ordering of the main network of the interpeptide hydrogen bonds which stabilizes the alpha-helical conformation (slightly distorted in the intial humid dark- and light-adapted state); light adaptation (cis-trans isomerization) of bacteriorhodopsin results in an increase of sorbed water in purple membranes. Dehydration of purple membranes decreases the reaction rate of cis-trans isomerization.

[Picosecond flash photolysis of Halobacterium halobium bacteriorhodopsin at room and low temperatures]. / Pikosekundnyi flesh-fotoliz bakteriorodopsina iz Halobacterium halobium pri komnatnoi i nizkikh temperaturakh.

The primary stage of photoexcitation of bacteriorhodopsin from Halobacterium halobium upon the action of ultrashort (tau equal to 25 ps) laser impulse of 530 nm wavelength and of energy 2.5.10(-3) J has been studied. The primary photoproduct with a maximum of 630 nm is shown to occur in the differential spectrum in a time less than 25 ps both at room temperature (+20 degrees C) and at a low temperature (-150 degrees C).