MEMBRANE-BOUND ENZYMES OF ERYTHROCYTES IN HUMAN MUSCULAR-DYSTROPHY - (NA++K+)-ATPASE, CA2+-ATPASE, K+-ATPASE AND CA2+-PARA-NITROPHENYLPHOSPHATASE

Four enzyme activities were studied in erythrocyte membranes from patients with Duchenne and congenital myotonic muscular dystrophy. (Na+ + K+)-stimulated, Mg2+-dependent adenosinetriphosphatase, measured in two different media, showed normal activity and ouabain inhibition, as did K+-stimulated p-nitrophenylphosphatase. The specific activity of Ca2+-stimulated p-nitrophenylphosphatase was twice normal in Duchenne membranes. Ca2+-stimulated, Mg2+-dependent adenosine-triphosphatase was augmented in membranes from both Duchenne and congenital myotonic muscular dystrophic patients. The cause of the increased activities may be the necessity for compensating an alteration in the calcium metabolism in the dystrophic erythrocytes. Several kinetic parameters of the two Ca2+-stimulated enzyme activities were studied in Duchenne and control membranes. Most were not changed, with the exception of the Na+-stimulation of Ca2+-ATPase. In Duchenne membranes two affinity sites were present with half maximal activating concentrations of 58 ± 4 and 4 ± 1 mM Na+. In control membranes only one affinity site was found with Ka = 26 ± 9 mM Na+. © 1979.