Analysis of the excited-state dynamics of 13-trans-locked-bacteriorhodopsin

Optical absorption spectra of 13-trans-locked-bacteriorhodopsin, which contains a chemically modified retinal chromophore inhibiting photoisomerization, were obtained at five temperatures. Analysis of the excited-state dynamics of the time-correlation function (tcf) of the modified wavepacket was made by the Fourier transform of the optical absorption spectra. Even though the photoisomerization of the chromophore was inhibited, the normalized tcf decayed rapidly until the level of about 10(-6) at 200 fs almost independently of the temperature. The ratio of the tcf between 13-trans-locked-bacteriorhodopsin and native bacteriorhodopsin displayed some oscillations. Its mean value was close to 1 until about 100 fs, and it increased, gradually up to the level of 10(0.5)-10(1) at about 200 fs. Namely, the excited-state dynamics of 13-trans-locked-bacteriorhodopsin appears globally quite similar to that of native bacteriorhodopsin up to about 100 fs, and the difference of them becomes slightly evident after 100 fs up to about 200 fs. Those data suggest that the excited-state dynamics of bacteriorhodopsin is not solely determined by the conformation change of the chromophore but also by another factor such as the movement of the microenvironment of the protein.