The aim of these experiments is to detect and measure internal motion in bacteriorhodopsin with 1 ps to 40 ps (initially) resolution over time regimes from 1 ps to 1 ms, as a probe of protein dynamics and protein- chromophore interaction. Experiments are proposed to study: 1) the amplitude and rate of overall motion of the bacteriorhodopsin chromophore in its light-adapted state and in intermediates J, K, and L; 2) the relaxation of strained conformations of the chromophore; 3) activation barriers to chromophore motion; 4) the temperature and solvent dependence of the binding site geometry; 5) the solvent viscosity dependence of chromophore relaxation; 6) proton coordination to a tyrosinate adjacent to the chromophore; and 7) activation volumes for chromophore evolution. Experiments to study low-temperature dynamics and room-temperature picosecond conformational evolution are also proposed for rhodopsin. Unique aspects of our approach are: 1) the accessibility of time regimes from 1 ps to 1 ms on a single instrument; 2) detection of internal motion by a probe of anisotropy decay that is not limited by the excited-state lifetime; 3) detailed measurement of relaxation rates of specific vibrational features; 4) accurate studies of the temperature and pressure dependence of relaxation rates. The approach proposed is to use a natural chromophore as a probe of protein dynamics. This problem is attacked by several picosecond laser techniques capable of generating specific and detailed information about structure and dynamics.
