THE FLUORESCENCE FROM THE TRYPTOPHANS OF RHODOPSIN

I NTRO DUCT1 ON THE CHROMOPHORE of rhodopsin, the visual pigment, is covalently attached to a protein, opsin. After initial photoisomerization of the chromophore, rhodopsin goes through a number of spectrally defined states, the intermediates of the bleaching of rhodopsin, before the chromophore becomes dissociated from the opsin. Guzzo and Pool [ 1,2] recently reported on the fluorescence from the chromophore of unbleached rhodopsin and of several of the intermediates. Ebrey [3] has described the fluorescence from the chromophore of bleached and reduced rhodopsin, N-retinyl-opsin. In opsin, as in all proteins which contain tryptophan, tryptophan is the principal fluorescing amino acid[4]. I n this report, the fluorescence from the tryptophans of opsin and of rod outer segments will be examined. Particular attention has been paid to the emission spectra of the fluorescing tryptophans and to the fluorescence yields before and after bleaching. In this way, it is possible to provide information about the environment of the tryptophans, about the quenching of fluorescence (presumably by energy transfer to the chromophore) and about the differences between rhodopsin in situ and in solution.