title: Thermodynamics of the binding of Ca2+ to porcine pancreatic phospholipase A2.
abstract: The binding of Ca2+ to porcine pancreatic phospholipase A2 was studied by batch microcalorimetry. Enthalpies of binding at 25 degrees C were determined as a function of Ca2+ concentration in buffered solutions at pH 8.0 using both the Tris-HCl and Hepes-NaOH buffer systems. The calorimetric results indicate that protons are released on calcium binding and that in addition to the binding of the active-site calcium, there appears to be weak binding of a second Ca2+. Results from potentiometric titrations indicate that this proton release on binding Ca2+ arises from a change in pK of a histidine(s) functional group. The thermodynamic functions delta G0, delta H0 and delta S0 for calcium binding to phospholipase A2 have been determined. These results are compared with literature data for Ca2+ complex formation with some small molecules and also the protein troponin-C.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002151:Calorimetry; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D010179:Pancreas / Q000201:enzymology*; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011199:Potentiometry; D011485:Protein Binding; D013552:Swine; D013816:Thermodynamics
chemical_list: D008024:Ligands; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium