The (Ca + Mg)-ATPase of reticulocytes

Rabbits were made reticulocytotic by repeated bleeding or by injection of phenylhydrazine. Up to reticulocyte levels of 70%, the baseline activity of magnesium-dependent calcium-stimulated adenosine triphosphatase ( ( Ca + Mg)-ATPase, EC 3.6.1.3.) of the red cell plasma membrane was not significantly changed. Maximal activity in the presence of calmodulin was significantly reduced, the stimulation by the activator falling from about 350% to about 50%.