The binding of corroded metallic ions to salivary-type proteins

Employing equilibrium dialysis, the binding ability of nickel, copper, and chromium from the corrosion of Biobond, Sybraloy, and Vitallium dental alloys in an inorganic saliva to glycoprotein, mucin, amylase, and lysozyme is reported. Binding was highest with copper to glycoprotein at 5.0 M Cu/M protein, followed by nickel at 1.2 M Ni/M protein, and by chromium at 0 M Cr/M protein. Tin products did not succumb to dialysis. The binding to all types of proteins exhibited molar ratios of about equal magnitudes except in lysozyme where binding was very low, most likely due to its high isoelectric point. Protein--protein interactions for amylase were higher, which hindered the nickel binding at lower protein concentrations. Peaks in glycoprotein binding vs pH behaviour occurred for copper at pH = 6 and for nickel at pH = 7. For glycoprotein and mucin, binding is taken to occur via the sialic acid carboxylate groups and for amylase via the imidazole groups of the histidine residues. It is thought that in order for copper to bind with the same number of sites as does occur with nickel, ligands of the form CuCl-CuCl2 are generated. The size of hexahydrate ligands of chromium are large which may not permit attachment onto binding sites.