Photochemistry and fluorescence of bacteriorhodopsin excited in its 280-nm absorption band

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Abstract
Photochemical and fluorescence studies were carried out, exciting bacteriorhodopsin (BR) (Halobacterium halobium) in its 280-nm absorption band. Energy transfer occurred, with a quantum yield of 0.7-0.8, from excited tyrosines and tryptophans to the retinyl chromophore. All of the tyrosine and 5-6 tryptophan residues were completely quenched by the transfer process while 1 tryptophan is unquenched and 1 is partially (.apprx. 80%) quenched. Energy transfer to the chromophore leads to a photocycle identical with that triggered in (light-adapted) BR by excitation within the visible absorption bands of the chromophore. The emissive properties of BR in the intact membrane are equal to those of a Triton X-100 solubilized BR monomer. The energy transfer data are discussed in terms of the available amino acid sequence and the electron density map of BR. Although such data cannot suggest a single fit between the sequence and the density map (5040 possibilities), they do provide a criterion for testing any specific model for the structure of BR.