Effect of hydrostatic pressure and pH value on the three-dimensional fluorescence spectrum of tyrosine solution with various concentrations of copper ion

Three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy was employed to characterize the effect of hydrostatic pressure on the fluorescence of tyrosine (Tyr) solution with various concentrations of copper ion (Cu2+) at pH 3.0, 7.4 and 9.0. Based on the mathematical statistics theory, the “mean”, “deviation”, and “gravity center” of the three-dimensional spectraʹs characteristic parameters were extracted. The three-dimensional fluorescence spectrum clearly revealed fingerprint-like properties of Tyr. The results showed that the fluorescence of Tyr solution became weak or was even quenched with the increase in the concentration of Cu2+ and increased with the hydrostatic pressure changing from 0.1 to 60 MPa. As the pH increased, the quenching of Cu2+ to Tyr became stronger. These results are consistent with those of two-dimensional fluorescence spectrum. This revealed that the principle and results of this method are applicable and valid. The significance of these results to Tyr is to overcome the overlapping spectra and distinguish the tyrosine from tryptophan, and provide fundamental references when tyrosine used as a probe to explore pressure induced protein structural changes.