The effect of ionizing radiation on tryptophan fluorescence of thymocyte and erythrocyte plasma membranes.

The effect of ionizing radiation on tryptophan fluorescence of thymocyte and erythrocyte plasma membrane preparations was studied. The intensity of tryptophan fluorescence decreased after applying radiation doses up to 15 Gy. The radiosensitivity of thymocyte membranes appeared to be higher than that of the erythrocyte ghosts. Tryptophan radiolysis did not significantly contribute to the effects of radiation. The fraction of tryptophan residues accessible for quenching by I- decreased from 0.87 in the untreated membranes to 0.63 and 0.49 in membranes after doses of 10 and 250 Gy, respectively. The effective quenching constant and the tryptophan fluorescence polarization increased after irradiation. The mechanisms producing these radiation-induced changes are discussed.