DEUTERIUM SUBSTITUTION EFFECT ON THE EXCITED-STATE DYNAMICS OF RHODOPSIN

We investigated the excited-state dynamics of the cis-trans photoisome rization of rhodopsin by analyzing deuterium substitution effects for hydrogen atoms bonded to C-11 and C-12 of the retinal chromophore by t he method of Fourier transform of optical absorption spectra (FTOA). P lotting the absolute value of the time correlation function of modifie d vibrational wave packet, we found that the deuterium substitution ef fects do not appear in the excited-state dynamics until about 20 fs af ter photon absorption, weakly appear in the time range 20-60 fs, signi ficantly appear in the time range 70-110 fs, and complicatedly appear in the time range 110-170 fs. By analyzing those deuterium substitutio n effects, we obtained a result that the concerted motions of hydrogen out-of-plane (HOOP) waggings at C-11 and C-12, which are found to exi st in native rhodopsin in the time range 20-60 fs, do not contribute t o the excited-state dynamics in its time range appreciably and that th e coupled motions of hydrogen atoms at C-11 and C-12, which are signif icantly coupled with the skeletal twisting motion of the chromophore i n the time range 70-110 fs, contribute to the excited dynamics in its time range substantially. The hydrogen motions after 110 fs contribute to the excited-state dynamics in a complicate way. This cis-trans pho toisomerization process of rhodopsin is basically similar to that of b acteriorhodopsin, which was obtained by the comparative analysis of th e FTOA of 13-trans-locked-bacteriorhodopsin with native bacteriorhodop sin.