The red cell membrane contains three different adenosine triphophatases.

Phosphorylated intermediates in the hydrolysis of ATP by human red cell membrane adenosine triphosphatases have been detected using [gamma-32-P]ATP. Intermediates formed in the presence of Mg2+ alone (MG-2+-ATPase), Mg-2+ and Na+ ((Na+,K+)-ATPase), and Mg-2+ and Ca-2+ (Ca-2+-ATPase) were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate at pH 2.4, indicating that these three ATPases are different molecular species. There are roughly 100, 150, and 400 copies per cell, respectively, of the three ATPases.