Radiation effects on erythrocyte membrane structure studied by the intrinsic fluorescence

The changes in the intrinsic fluorescence, primarily from tryptophan residues, of sheep erythrocyte membranes following X-irradiation (0--4000 R) were investigated. The experiments showed that there was (1) a decrease in the intensity of fluorescence with increasing dose of X-rays, (2) a small shift of fluorescence emission to longer wavelengths, (3) a decrease in the fluorescence polarization, and that (4) treatment of membranes with a perturbing solvent, 2-chloroethanol, can eliminate the effects of X-rays. The amount of tryptophan in the membranes was not altered after X-irradiation. It was also shown that sulphydryl reagents, N-ethylmaleimide and 2,2'-dithiodipyridine, induced similar fluorescence changes. From these results it was concluded that the fluorescence changes could result from a change in the environment surrounding tryptophan residues, from being relatively non-polar to being more polar, implying that conformational changes of membrane proteins are brought about by low doses of X-rays.