Stimulation of calcium transport in inside-out vesicles of human erythrocyte membranes by a soluble cytoplasmic activator

Transport of Ca²⁺ by inside-out vesicles requires both Mg²⁺ and ATP and can be linear over 16 min at 37°C. This basal rate of transport may be doubled however by an activator found in membrane-free erythrocyte hemolysate. This activator is probably the same protein(s) which has been shown to activate (Ca²⁺ + Mg²⁺)-ATPase in erythrocyte membrane fragments (Bond, G.H. and Clough, D.E. (1973) Biochim. Biophys. Acta 323, 592–599).