FLUORESCENCE DECAY KINETICS OF TYROSINATE AND TYROSINE HYDROGEN-BONDED COMPLEXES

We have examined the time-resolved fluorescence of aqueous tyrosine in the presence of high buffer base concentrations, to model the interactions between tyrosyl residues and potential proton-accepting side chains in proteins. The decay kinetics were not consistent with the formation of excited-state tyrosinate by proton transfer. Rather they indicated the presence of ground-state hydrogen-bonded complexes that persisted in the excited-state. Fluorescence properties of the tyrosine hydrogen-bonded complexes were correlated with the pK(a) of the proton acceptor and compared with those of tyrosinate. We conclude that the results have significance in the interpretation of fluorescence data from proteins.