FLUORESCENCE OF TYROSINE AND TRYPTOPHAN IN PROTEINS USING ONE-PHOTON AND 2-PHOTON EXCITATION

We examined the emission spectra of tyrosine- and tryptophan-containin g proteins using one-photon (270-310 nm) and two-photon (565-610 nm) e xcitation. Emission spectra for two-photon excitation of native and de natured human serum albumin and of three purine nucleoside phosphoryla ses indicated an absence of the tyrosine emission normally seen for on e-photon excitation below 290 nm. We examined the one-photon and two-p hoton excitation spectra of tyrosine-tryptophan mixtures to determine the origin of selective excitation of the tryptophan residues. These r esults confirmed a short-wavelength shift of the tyrosine two-photon e xcitation spectrum relative to that of tryptophan, as recently reporte d by Rehms and Callis (1993) Chem. Phys. Lett. 208, 276-282.