Fluorescence-polarization spectrum and electronic-energy transfer in proteins

Abstract

propylene glycol solution at -700, excited with unpolarized light.2. Phenol, cresol and tyrosine show a simple spectrum, consisting of a negative polarization region with a minimum value of -0-065 at 235 mF, and a positive region with a maximum of 0-22 at 275 mp and longer wavelengths.3. Indole, N-methylindole and tryptophan show no negative polarization at any wavelengths.In the region of the longest wavelength-absorption band two maxima are present at 270 and 305 m,u and a minimum at 295 m,u.It is shown that at least two electronic transitions are required to describe these effects, one of these transitions corresponding to the spike or shoulder observed in absorption at 295 m1i.4. N-Glycyltryptophan has a spectrum similar to the other indole derivatives but for the existence of an additional sharp polarization band with maximum at 290 mp, which appears connected with the presence of a peptide bond.5. Concentration-depolarization measurements show that the distance R at which the probability of transfer of the excitation equals the probability of emission is 17A for phenol molecules.6. Concentration-depolarization measurements on indole solutions show that R = 17A if the fluorescence is excited with light of wavelength shorter than 295 m,, but that excitation with longer wavelengths is not followed by transfer with very much lower efficiency.7. Measurements of the fluorescence spectrum in mixtures of phenol (1M) and indole (001-02M) show that phenol can transfer its energy to indole with R 18-5A.This paper describes the fluorescence-polarization spectrum of two classes of globular proteins.Class A proteins containing phenylalanine and tyrosine but no tryptophan.These proteins (Teale & Weber, 1959;