TIME-RESOLVED EMISSION SPECTRA OF TRYPTOPHAN AND PROTEINS FROM FREQUENCY-DOMAIN FLUORESCENCE SPECTROSCOPY

摘要

We report measurements of time-resolved emission spectra of N-acetyl-L-tryptophanamide (NATA), adrenocorticotropic hormone (ACTH, residues l-24), and of S. Nuclease. These spectra were calculated from the frequency-response of the emission, measured at several wavelengths across the emission spectra. Measurements were performed on samples not quenched and quenched by acrylamide, the latter providing additional information on the short time events. The time-resolved center-of-gravity does not decay as a single exponential. At least two spectral relaxation times are needed to account for the present data. NATA and ACTH each display relaxation times near 50 and 800 ps, which may be characteristic of exposed tryptophan residues. S. nuclease displayed slower relaxation times near 0.5 and 10 ns, which probably reflect the dynamic protein matrix which surrounds the residue.