FT-IR and Resonance Raman Studies of Structural Changes of Bacteriorhodopsin under Dehydration

Abstract

FT-IR difference spectroscopy has been used to study the influence of water on the structure of both the retinal and protein in the dark-adapted purple membrane at low temperature. Assignment of chromophore vibration was made on the basis of FT-IR data and by comparison with resonance Raman results. We established that the BR506 form, generated in a dehydrated purple membrane comes from the parent BR548 from. The present FT-IR difference measurements in a two-channel mode showed that the retinal configuration of BR506 is the all-trans, while according to the earlier resonance Raman data the conformation of its retinal is 13-cis. This discrepancy is explained in the present paper.