Microcalorimetric investigations of the interactions of small ions with arterial elastin

The enthalpies of interactions of porcine arterial elastin with alkali metal and alkali earth halides and sulphates were investigated by means of flow microcalorimetry and the stoichiometry measured using radiotracer techniques. In aqueous solutions, all alkali earth halides interacted exothermically at concentrations ranging from 0.01 to 2.5M. All the alkali metal halides, particularly NaCl, exhibited complex concentration-dependent interactions, exothermic at low concentrations and endothermic at high concentrations. Both the anion and cation contributed to the response, although the anion seemed to dominate. SO4(-2) interacted most strongly of the anions tested. All interactions were reversible in the sense that repeat experiments gave identical results, but the enthalpy of "adsorption" was generally different from that of "desorption." The enthalpy of interaction depended on the conformation of the elastin in a salt-specific manner. For example, CaCl2 and MgCl2 interacted similarly in water but very differently in 1:1 water:methanol.