Infrared studies of water induced conformational changes in bacteriorhodopsin

Fourier transform infrared difference spectroscopy has been used to study the effect of water on the conformation of bacteriorhodopsin. The infrared spectra as a function of water content show a conformational change at about 0.06 g H2O/g bacteriorhodopsin. By an interference method the thickness of the sample was measured and shows similar behavior as a function of water content. This study gives insight into the process of water absorption by purple membrane. The observations are in good agreement with those found for other proteins.