A thermodynamic and electron paramagnetic resonance study of structural changes in calmodulin induced by aluminum binding.

Bovine brain calmodulin binds 3 mol aluminum per mol protein with dissociation constants in range of 10(-7) to 10(-6) molar. EPR spectra of spin-labelled calmodulin provide data indicating that aluminum binding causes decreased probe immobilization as compared to the effects of calcium binding. This result of aluminum binding indicates that A1-calmodulin is a more random, open polypeptide relative to the structure of Ca2+-calmodulin. Calorimetric measurements of aluminum binding provide data showing that the first mol of aluminum bound is accompanied by the largest enthalpic change (-3.9 kcal mol-1), whereas binding of the second and third mol of aluminum are each entropically driven.