Abstract
The structural alterations which occur in bacteriorhodopsin (bR) during dark adaptation (BR sub(570) arrow right BR sub(548)) and the primary phototransition of the dark photocycle (BR sub(548) arrow right K super(D) sub(6) sub(1) sub(0)) have been investigated by Fourier transform infrared and UV difference spectroscopy. Possible contributions of tyrosine to the Fourier transform infrared difference spectra of these transitions were assigned by incorporating ring per-deuterated tyrosine into bR. Based on these data and UV difference measurements, the authors conclude that a stable tyrosinate exists in BR sub(570) at physiological temperature and that it protonates during formation of BR sub(548).