Abstract

The fluorescence anisotropy of tryptophanyl residues in proteins is used as a probe of protein motion. We have recently shown⁽¹⁾ that the short life time (200 fs - 10 ps) region of the fluorescence anisotropy of tryptophan in solution is dominated by an electronic relaxation process, which has the potential to obscure molecular motion. The question arises as to the relevance of this result for the behavior of tryptophanyl residues in proteins. To address this question we have examined the subpicosecond fluorescence anisotropy of tryptophanyl residues in two very different enviroments - exposed to the solvent in melittin, a 26 amino acid peptide, and buried in a hydrophobic region in apoazurin purified from the bacteria Pseudomonas aeruginosa. Measurements were made by ultraviolet fluorescence upconversion described elsewhere⁽¹⁾. Samples were degassed and flowed in absence of air. Concentrations were adjusted so the optical density at the excitation wavelength was between 0.6 and 1.0 for a 1mm pathlength.

© 1990 Optical Society of America