ATP/ATPase and flux activities in human red blood cells

ATP synthase [E.C.3.6.1.34] of 16 subunits and of CuA CuB prosthetic groups is also known as 'coupling ATPase', H+-ATPase (Hajjawi, 2011; 2012a). This enzyme can utilize the energy released by the movement of protons down   H+ to energize the synthesis of ATP. The enzyme consists of three subunits, an α subunit (112.5kDa) that couples ATP hydrolysis and ion transport, β subunit (45 kDa) and a small proteolipid γ subunit (10kDa) that copurifies with the protein but does not appear to be required for ATPase activity (Hardwicke and Fretag, 1981; Grüber, 2001). The α, β and γ subunits are in a ratio of 1:1:1. ATP has several known functions in the red blood cell (RBC). It fuels the Na+ pump (Sachs, 2003; Gusev and Ivanova, 2004), which is thought to be involved in regulation of cell volume (Huber et al., 2001; Brugnara, 2003), and the Ca2+ pump (Romero and Romero, 2003), without which the cells take up Ca and subsequently shrink because of activation by Ca2+ of a K+ channel in the membrane (Gibson and Ellory, 2003). In these cases, transfer of energy from ATP hydrolysis to the actively transported ions appears to involve specific ATPases in the membrane. ATP is also required for maintenance of normal cell structure; ATP depletion causes changes in the morphology (Gibson et al., 2000; Hajjawi, 1012b) and in the rheological properties (Henkelman et al., 2010) of the RBCs. These changes have clinical significance since RBCs low in ATP have poor post- transfusion viability (Yoshida and Shevkoplyas, 2010).Thus, RBC ATP and ATPase activities play an important role in research on the mechanisms of active transport and on the integrity of cell structure.