EFFECT OF PHOSPHATE ION ON FLUORESCENT CHARACTERISTICS OF TYROSINE AND ITS CONJUGATE BASE

Abstract—The UV fluorescence spectrum of tyrosine (Tyr) is markedly affected by the interaction with phosphate ion. In order to elucidate the mechanism of the specific fluorescence quenching by phosphate and the simultaneous appearance of a new emission, the effect of phosphate on the spectro-scopic characteristics of Tyr was investigated. Employing a fluorimetric method, we have obtained the following results. Namely, potassium phosphate was found to enhance the fluorescence intensity of tyrosinate ion. When Tyr is excited in the phosphate-containing solution, the emission with a peak around 345 nm is observed besides the normal fluorescence of Tyr around 303 nm with a reduced quantum yield. The abnormal emission may be ascribed to the tyrosinate ion in the excited state resulting from the deprotonation of the phenolic OH group of the excited Tyr. although the tyrosinate ion in the ground state is not predominant in the aqueous solution examined.