[Investigation of the effects of dehydration on bacterial rhodopsin by laser resonance Raman spectroscopy]

Abstract

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.