UV resonance Raman spectroscopy of TTR(105–115): determination of the pKa of tyrosine

Abstract

The 11-residue peptide fragment from transthyretin (TTR(105–115)) has been investigated using UV resonance Raman spectroscopy. Excitation at 239.5 nm reveals selective enhancement of scattering from two Tyr residues. The titrating behavior of the tyrosines is followed through the change in the Y8a band (1617 cm⁻¹) frequency as a function of pH, and a pK_a = 10.2 ± 0.2 is obtained. This is compared to the value of 9.1 ± 0.2 for the pK_a of aqueous Tyr also obtained in the present study. The pK_a difference observed here, along with observations in the ν(OH) region, suggest that the two Tyr residues in the peptide probe two distinct microenvironments.