Abstract

Spectroscopic properties of tyrosine residues may be employed in structural studies of proteins. Here we discuss several different types of UV–Vis spectroscopy, like normal, difference and second-derivative UV absorption spectroscopy, fluorescence spectroscopy, linear and circular dichroism spectroscopy, and Raman spectroscopy, and corresponding optical properties of the tyrosine chromophore, phenol, which are used to study protein structure.

Introduction

Fluorescence and other spectral parameters of aromatic chromophores in proteins, tryptophan, tyrosine (Tyr) and phenylalanine, may be used as probes of protein structure. Using Tyr is an attractive choice because its chromophore, phenol, is expected to exhibit substantial responses to environmental changes (Fornander et al. 2014). We have found it interesting to review the development of structural studies of proteins based on detection of different spectroscopic features of tyrosines in the UV–Vis range, from the earliest investigations using UV absorbance measurements (Crammer and Neuberger 1943; Shugar 1952) to more recent resonance Raman (Larkin 2011; Reymer et al. 2014) or linear dichroism (Reymer et al. 2009) spectroscopy studies.

First, we recall the basic principles of different methods in UV–Vis spectrometry. We then describe properties of Tyr and related model compounds, i.e., phenol, para-cresol (p-cresol) and N-acetyl-l-tyrosine amide (N-Ac-Tyr-NH₂) as revealed by different UV–Vis spectroscopies. In Part 2, we present selected applications of UV–Vis spectrometry of tyrosines to probe protein structures.