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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 was found to follow the same pattern of activation by Ca2+ as the control membranes. However, the Ca2+-ATPase activity in DMD and some DMD-carrier preparations was substantially elevated compared with controls. To characterize further the elevated Ca2+-ATPase activity found in DMD-patient ghost membrane preparations, we estimated kinetic parameters using both fine adjustment and weighting methods to analyse our experimental data. It was established that 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 degrees C, and in DMD and DMD-carrier preparations an elevated Ca2+-ATPase activity was detected at all temperatures. Above 20 degrees 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.
Insights
Erythrocyte membrane Ca2+-ATPase activity is elevated in Duchenne muscular dystrophy (DMD) patients and carriers, suggesting altered membrane properties. This finding may relate to the generalized physicochemical changes observed in DMD.
Area of Science:
- Biochemistry
- Cell Biology
- Genetics
Background:
- Duchenne muscular dystrophy (DMD) is associated with numerous membrane abnormalities.
- Erythrocyte membranes are a model system to study these alterations.
Purpose of the Study:
- To investigate the Ca2+-stimulated Mg2+-dependent ATPase (Ca2+-ATPase) activity in erythrocyte membranes from DMD patients and carriers.
- To compare these activities with those of normal controls.
Main Methods:
- Assay of Ca2+-ATPase activity in erythrocyte ghost membranes.
- Kinetic parameter analysis (Vmax, Km) using fine adjustment and weighting methods.
- Investigation of temperature-dependent activity and activation energy via Arrhenius plots.
Main Results:
- Ca2+-ATPase activity was substantially elevated in DMD patients and some DMD carriers compared to controls.
- The increased activity was attributed to a higher Vmax, not a change in Km.
- Elevated Ca2+-ATPase activity was observed across all tested temperatures in DMD and carrier preparations.
- Activation energy below 20°C was elevated in DMD and carrier preparations.
Conclusions:
- Duchenne muscular dystrophy and its carriers exhibit significantly altered erythrocyte membrane Ca2+-ATPase activity.
- These alterations, particularly the increased Vmax and temperature-dependent kinetics, suggest underlying changes in membrane physicochemical properties.
- The findings support the hypothesis of generalized alterations in the membrane lipid domain in DMD.