Fourier transform infrared deconvoluted spectra of bacteriorhodopsin and the N intermediate were compared with the N/BR infrared difference spectrum. In the amide I, clear changes in the bands at 1666 cm-1, assigned to α(II) helices, 1659 cm-1 assigned to α(I) and α(II) helices, and 1652 cm-1, assigned to both α(I) helices and unordered structures, were found. These changes could arise from conversion of some α(II) into α(I) helices. Variations in the bands at 1692 and 1683 cm-1, corresponding to reverse turns, were also detected. The side chains of Tyr (band at 1517 cm-1) and Phe (band at 1498 cm-1) were found to change in going from BR to N. In the carboxylate region, no band was detected at 1737 cm-1 in the deconvoluted spectra that could correspond to the peak observed in the difference spectrum. It is argued that resolution-enhancement methods used along with difference spectra provide more detailed insights into the conformational changes occurring between photocycle intermediates.
|Publication status||Published - 28 Jul 1996|