Electron spin resonance studies of membrane proteins in erythrocytes in myotonic muscular dystrophy

A sulfhydryl group specific spin label has been used to study membrane proteins in erythrocyte ghosts from patients with myotonic muscular dystrophy (MyD). The resulting electron spin resonance spectra of labeled permeable MyD and control ghosts demonstrate two chief populations of sulfhydryl groups, one weakly immobilized, the other strongly immobilized. Approximately one-third of the labeled sulfhydryl groups are in weakly immobilized sites which, based on their nitrogen hyperfine splitting value and their accessibility to both spin label and ascorbate, appear to be located near the membrane surface in a highly polar environment. Strongly immobilized sulfhydryl groups appear to be located both at the membrane surface and deep within the lipid bilayer. While the linewidths of each class of sites are equal in control and MyD membranes, the ratio of the spectral amplitude of the spin label attached to weakly immobilized sites to that of strongly immobilized sites is significantly greater in MyD membranes (P ≅ 0.001). This effect is due to a decreased incorporation of the spin label into the strongly immobilized sulfhydryl group sites and suggests that membrane organizational or protein conformational differences exist between MyD and control erythrocyte membranes.