Ultraviolet fluorescence of the aromatic amino acids

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Abstract
The fluorescence-excitation spectrum, fluorescence spectrum and quantum yield are proposed as criteria to characterize a molecular species in solution as a fluorescent entity. The fluorescence spectra of phenylalanine, tyrosine and tryptophan in neutral water solution consist of single bands in the UV with maxima at 282, 303, and 348 m[mu] respectively. The fluorescence-excitation spectra determined from 200 to 320 m[mu] correspond accurately to the known absorption spectra of the amino acids, showing the constancy of the quantum yield over the range of wavelengths investigated. The quantum yields ([plus or minus]1%) in neutral water solutions are 4% for phenylalanine, 21% for tyrosine and 20% for tryptophan. The possibility of electronic energy transfer among the aromatic residues in proteins and to the heme in hemoproteins is discussed.
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