title: The influence of methanol on the interactions of calcium with the pyridine nucleotides.
abstract: The interactions of calcium with NAD+, NADH, NADP+ and NADPH in a 50% (by volume) methanol/water mixture (pH 7, 25 degrees C) were studied by calorimetry. The association constants for 1:1 complex formation were found to be 6.6 +/- 0.2, 270 +/- 76, 18 +/- 3 and 98 +/- 10 for NAD+, NADH, NADP+ and NADPH, respectively. Comparing these to the association constants for an aqueous system reveals that as the polarity of the solvent system is decreased the interactions involving NAD+, NADP+ and NADPH are all decreased. In contrast, the interaction involving NADH is markedly increased. All the interactions were found to be endothermic.
mesh_terms: D002118:Calcium; D002151:Calorimetry; D000432:Methanol; D009243:NAD; D009249:NADP; D013816:Thermodynamics
chemical_list: D009243:NAD; D009249:NADP; D002118:Calcium; D000432:Methanol