Equilibrium cooperative binding of calcium and protons by sarcoplasmic reticulum ATPase.
The cooperative equilibrium binding of Ca2+ by sarcoplasmic reticulum ATPase, as modulated by pH, is analyzed by statistical mechanical treatment of a theoretical model. The model consists of four equivalent subunits, in the form of a square, with nearest-neighbor interactions. Each subunit has one site for binding of one Ca2+ or one proton, but not both. Binding of either ligand on a subunit induces a conformational change in the subunit that alters its interaction with its two neighbors. The model gives good agreement with experimental binding data. It should prove useful as a starting point in the analysis of steady-state ATPase activity as a function of Ca2+ and H+ concentrations.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009132:Muscles / Q000201:enzymology; D011485:Protein Binding; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D000252:Calcium-Transporting ATPases; D002118:Calcium