On the use of the spin labeling technique in the study of erythrocyte membranes

ESR spectra and scanning electron micrographs of human erythrocytes spin labeled with the conventional stearic acid nitroxide substituted at the 5-position have been obtained over a range of label-to-lipid ratios. While morphological changes as previously reported (Bieri, V. G., Wallach, D. F. H. and Lin, P. S. (1974) Proc. Natl. Acad. Sci. U.S. 71, 4797-4801) are reproduced, it is shown that at label-to-lipid ratios of 1:10 or less the basic ESR spectrum is not significantly affected. At low label concentrations the spin labeling technique is a viable one and can be used to investigate membrane properties.