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 degrees C. This basal rate of transport may be doubled however by an activator found in membrane-free erythrocyte hemolysate. This activatior 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).