title: Effect of hemolysate on calcium inhibition of the (Na+ + K+)-ATPase of human red blood cells.
abstract: The sensitivity of the (Na+ + K+)-ATPase in human red cell membranes to inhibition by Ca2+ is markedly increased by the addition of diluted cytoplasm from hemolyzed human red blood cells. The concentration of Ca2+ causing 50% inhibition of the (Na+ + K+)-ATPase is shifted from greater than 50 microM free Ca2+ in the absence of hemolysate to less than 10 microM free Ca2+ when hemolysate diluted 1:60 compared to in vivo concentrations is added to the assay mixture. Boiling the hemolysate destroys its ability to increase the sensitivity of the (Na+ + K+)-ATPase to Ca2+. Proteins extracted from the membrane in the presence of EDTA and concentrated on an Amicon PM 30 membrane increased the sensitivity of the (Na+ + K+)-ATPase to Ca2+ in a dose-dependent fashion, causing over 80% inhibition of the (Na+ + K+)-ATPase at 10 microM free Ca2+ at the highest concentration of the extract tested. The active factor in this membrane extract is Ca2+-dependent, because it had no effect on the (Na+ + K+)-ATPase in the absence of Ca2+. Trypsin digestion prior to the assay destroyed the ability of this protein extract to increase the sensitivity of the (Na+ + K+)-ATPase to Ca2+.
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D006461:Hemolysis; D006801:Humans; D008565:Membrane Proteins / Q000097:blood; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000097:blood
chemical_list: D008565:Membrane Proteins; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium