Efficiency of energy transfer by resonance in quenching of protein fluorescence by dyes

Considering the quenching of tryptophan fluorescence of bovine serum albumin by various dyes as an example, it is shown that overlap of radiation and absorption spectra does not necessarily lead to energy transfer by resonance. No correlation is revealed between the limiting quenching and the Forster overlap integral. Quenching can occur even in the absence of overlap. The magnitude of energy transfer is markedly lower than that of quenching owing to competing processes, namely, excitation deactivation by the dye and, probably, by the protein itself which undergoes conformation upon sorption of the dye. Negatively charged and neutral dyes posses, on the average, a higher quenching activity relative to albumin than do positively charged dyes.