Rhodopsin and its thermal intermediates: Fast structural fluctuations in their protein component

The tryptophan residues of bovine rhodopsin have been employed as intrinsic fluorescent probes for investigating the dynamics of rhodopsin and of the thermal intermediates of its bleaching at low temperature. A fast depolarization of the fluorescence of the tryptophans on the nanosecond time scale has been observed for all cases. The fluorescence spectra for the various intermediates shift progressively to the red as a function of time following excitation with nanosecond light pulses. It is inferred that rhodopsin possesses flexibility in the vicinity of its tryptophans that permits rapid structural fluctuations to take place.