UV RESONANCE RAMAN SATURATION SPECTROSCOPY MEASURES PROTEIN AROMATIC AMINO-ACID EXCITED-STATE RELAXATION RATES

We demonstrate the utility of the new technique of UV resonance Raman saturation spectroscopy (Teraoka et al. J. Am. Chem. Soc. 1990, 112, 2892) for studying tryptophan and tyrosine excited-state relaxation rates in proteins. This technique monitors the ground-state population during UV pulsed laser excitation. It reports on ground-state recovery rates for aromatic amino acid residues which depend upon energy-transfer processes and photoionization quantum yields. We demonstrate the dependence of the relaxation rates on aromatic amino acid environment in lysozyme, myoglobin, and glucagon and examine energy transfer between aromatic amino acid residues in a tryptophan-tyrosine dimer. In contrast to aromatic amino acid solution studies, we find little photoionization in the proteins studied. This technique is of general utility for studying relaxation rates of chromophores, even those with weak fluorescence such as phenylalanine and tyrosine in proteins containing tryptophan residues. We discuss the utility of this technique for future biological and chemical applications. We also demonstrate the dependence of the aromatic amino acid residue Raman cross sections to the protein residue environment. © 1990, American Chemical Society. All rights reserved.