Characteristics of an adenosine triphosphatase in erythrocyte membranes stimulated by 2,4-dinitrophenol

Studies were made of the stimulation by 2,4‐dinitrophenol (DNP) of an adenosine triphosphatase (ATPase) in stromata of human erythrocytes. Activation by 2,4‐dinitrophenol occurs in the range 10−5 to 10−3 M and was seen in whole cells, ghosts reconstituted with Mg and ATP, and in osmotic ghosts prepared at a low ratio of cells to water. Phloretin and phloridzin also activated the DNP sensitive system but inhibited it at higher concentrations. DNP increased the Km and Vmax values of the enzyme equally. The DNP sensitive and Na+ + K+ sensitive enzymes of the stromata were compared. The activities of the two ATPases are additive, require the presence of Mg++ and require that the substrate be located at the inner surface of the membrane. The two enzymes differ in their substrate specificity, in their sensitivity to inhibition by ouabain and phloretin and in their sensitivity to some factor in hemolysates. The possible roles of this system in the erythrocyte were discussed.