(Ca ++ + Mg ++ )‐ATPase of red cells in Duchenne and myotonic dystrophy

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Abstract
Red cell (Ca++ + Mg++)-ATPase was investigated in Duchenne and myotonic dystrophy patients. Saponin-lysed red cells of patients with Duchenne dystrophy displayed slightly higher (Ca++ + Mg++)-ATPase activity (66.2 ± 2.6 ±moles Pi [inorganic phosphorus] per 2 hours per milliliter cells) than age-matched male controls (54.3 ± 2.4 ±moles Pi per 2 hours per milliliter cells). The activity of the enzyme in myotonic dystrophy patients was somewhat lower (59.6 ± 1.3 μnoles Pi per 2 hours per milliliter cells) than in controls (66.7 ± 1.6 ±moles Pi per 2 hours per milliliter cells). In all cell types, a cytoplasmic activator protein is present, which stimulated the (Ca++ + Mg++)-ATPase of hypotonically isolated membranes. In age-matched Duchenne controls, the membrane enzyme was maximally stimulated by the activator, increasing from 14.4 ± 0.5 ±moles Pi per 2 hours per milliliter cells to 28.5 ± 1.4 ±moles Pi per 2 hours per milliliter cells. Duchenne (Ca++ + Mg++)-ATPase was enhanced from 15.8 ± 0.7 ±moles Pi per 2 hours per milliliter cells in the membrane to 33.3 ± 1.8 ±moles Pi per 2 hours per milliliter cells by the activator. Similarly, myotonic (Ca++ + Mg++)-ATPase activity was augmented from 13.7 ± 0.5 ±moles Pi per 2 hours per milliliter cells to 29.4 ± 1.5 ±moles Pi per 2 hours per milliliter cells by the activator, whereas enzymes from age-matched controls displayed a stimulation from 15.0 ± 0.6 ±moles Pi per 2 hours per milliliter cells to 36.2 ± 1.7 ±moles Pi per 2 hours per milliliter cells in the presence of their own activator. The extent of the enzyme stimulation by the activator was independent of the source of its origin in all cases, suggesting that the differences observed in the (Ca++ + Mg++)-ATPase from patients and controls were more likely related to differences in membrane structure than to alteration in the activator protein.