Erythrocyte-ghost Ca2+-stimulated Mg2+-dependent adenosine triphosphatase in Duchenne muscular dystrophy

Abstract

The Ca2+-stimulated Mg2+-dependent ATPase activities (Ca2+-ATPase) of erythrocyte ghost membranes from patients with Duchenne muscular dystrophy (DMD) and carriers of DMD were compared with activities of normal controls. The Ca2+-ATPase activity of DMD-patient ghost preparations followed the same pattern of activation by Ca2+ as the control membranes. The Ca2+-ATPase activity in DMD and some DMD-carrier preparations was substantially elevated compared with controls. To further characterize the elevated Ca2+-ATPase activity found in DMD patient ghost membrane preparations, kinetic parameters were estimated using both fine adjustment and weighting methods to analyze experimental data. In both DMD and DMD-carrier preparations, the increase in Ca2+-ATPase activity was reflected by a significant increase in Vmax rather than by any change in Km. The response of the membrane Ca2+-ATPase activity to changes in temperature was also investigated. In all preparations a break in the Arrhenius plot occurred at 20.degree. C, and in DMD and DMD carrier preparations an elevated Ca2+-ATPase activity was detected at all temperatures. Above 20.degree. C the activation energy for all types of preparation was the same, whereas below this temperature there appeared to be an elevated activation in DMD and DMD-carrier preparations compared with normal controls. The concept that a generalized alteration in the physicochemical nature of the membrane lipid domain may be responsible for the many abnormal membrane properties reported in DMD is discussed.