Spin-label studies of the lipid and protein components of erythrocyte membranes. A comparison of electron paramagnetic resonance and saturation transfer electron paramagnetic resonance methods.

We have used both a protein spin label and a lipid spin probe to study some of the slow motions of proteins and of lipids, respectively, in intact erythrocyte membranes. Three electron paramagnetic resonance (EPR) methods, conventional (V1) EPR, second harmonic out-of-phase absorption saturation transfer (ST) EPR (V'2), and first harmonic out-of-phase dispersion ST EPR (U'1) were used to compare the experimental methods and spectral sensitivities with different kinds of molecular motions in human erythrocyte membranes under different experimental conditions. The results show that the V'2 display is relatively more sensitive to the protein motion, while the U'1 display appears more sensitive to the lipid motions, and the V'2 display is substantially more convenient to obtain than the U'1 display.