Modifications induced by zinc, cadmium and mercury acetates on hexokinase in aqueous solutions

Preferential interactions of hexokinase with solvent were studied in aqueous solutions of Zn2+, Cd2+ and Hg2+ acetates. In addition, these preferential interactions were correlated with protein solubility in the solvent media and the influence of salts on the tertiary structure of hexokinase using viscometric studies. The viscometric results show that hexokinase can undergo a conformational change at 2·5mM of Zn2+ and Cd2+ salts, whereas the effect of Hg2+ acetate on hexokinase is evident at ten times smaller concentrations. The interaction parameter is always positive for all the salts studied, indicating that interaction of the salt and protein is thermodynamically unfavourable, although this effect is lower for the Zn2+ salt. The transfer free energy parameter and solubility data show that for hexokinase zinc acetate is a salting-in agent, mercury acetate is a salting-out agent and cadmium acetate cannot be clearly classified.