Stearic acid methyl ester spin-labels with the paramagnetic center located at the 5, 12, and 16 positions on the fatty acid alkyl chain have been used to study the erythrocyte membrane from patients with myotonic muscular dystrophy, a systemic disorder inherited as an autosomal dominant trait. It has been demonstrated that the physical state of the erythrocyte membrane from patients with this disease is different from that of normal controls. At all levels of penetration into the membrane probed by the spinlabel, myotonic membranes were more fluid and less polar than control membranes. The overall average values of the order parameter, S, and the nitrogen isotropic coupling constant, ON, obtained with the 5, 12, and 16 labels were respectively (0.65, 15.9 G), (0.59, 15.5 G), and (0.26, 13.9 G) in normal membranes while the parameters were respectively (0.61, 15.8 G), (0.58, 15.3 G), and (0.25, 13.8 G) for the three labels in myotonic erythrocytes. The fluidity difference between normal and myotonic membranes is most apparent near the surface of the membrane while the polarity difference is approximately constant at various depths within the membrane. These results support the concept of myotonic muscular dystrophy as a diffuse membrane disease.
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