Infrared emission from photoexcited bacteriorhodopsin: studies by Fourier transform infrared spectroscopy

In the present work, using Fourier transform-infrared (FT-IR) technique we were able to register the infrared emission from a wet film of bacteriorhod opsin (bR) under continuous illumination with visible light (from a 100-W X enon lamp) at room temperature. Emitted radiation is not induced by tempera ture rise, it has a discrete spectrum in the infrared range from 400 up to 4000 cm(-1). There are the bands relating to a retinelidene chromophore as well as to a protein matrix. By comparing these results with the resonance Raman and IR-absorption data the majority of stretching vibrations can be i dentified. The agreement in the frequency of bands assigned to the chromoph ore of bR is very good, whereas the difference occurs in the intensity dist ribution among the characteristic bands. It was found that the IR-emission spectra displayed two C=C stretching frequencies at 1528 and 1516 cm(-1) at tributed to the parent, bR(568), and K-610-intermediate states, respectivel y, whose intensity strongly depended on a varying of a wavelength of the in cident light. The data presented here give new spectral information on the molecular processes occurring in the bR molecule during optical excitation. (C) 2001 Elsevier Science B.V. All rights reserved.