Equilibrium dialysis and ultrafiltration studies of calcium and phosphate binding by human salivary proteins. Implications for salivary supersaturation with respect to calcium phosphate salts

Abstract

Previous ultrafiltration studies indicated that up to one-half of the calcium and two-thirds of the phosphate in human salivary secretions may be bound by salivary proteins. Since this binding is an important variable in determining the extent of salivary supersaturation with respect to calcium phosphate salts, and since the amount of binding reported is surprisingly large, calcium and phosphate ion-binding by salivary macromolecules has been reexamined. From experiments using equilibrium dialysis, it was found that (1) the fraction of salivary calcium involved in macromolecular complexes ranges from a few percent for unstimulated secretions, to no more than about 10% for stimulated glandular salivas, and (2) salivary proteins do not bind phosphate ions to any significant extent. These findings, and experiments using an improved ultrafiltration membrane, indicate that the earlier results were artifacts of the ultrafiltration technique. Fractionation of salivary proteins, followed by equilibrium dialysis measurements, showed that the anionic proline-rich proteins and a basic proline-rich glycoprotein are responsible for most of the calcium binding now observed. The finding that macromolecular complexes of salivary calcium and phosphate have been overestimated in the past, leads to the conclusion that salivary calcium and phosphate ion activities in stimulated salivary secretions may be up to 50 to 100% higher than previously thought. Revised values were therefore used to recalculate the degree of salivary supersaturation with respect to calcium phosphate salts. The results indicate that stimulated salivary secretions are supersaturated with respect to dicalcium phosphate dihydrate; this is a substantially greater degree of supersaturation than previously reported.

Development of Carious-Like Lesions in Partially Saturated Lactate Buffers

“…1985], as well as in the characterization of saliva [Hay et al, 1982]. These plots are solubility diagrams expressed in terms of the chemical potentials of phosphoric acid and cal cium hydroxide.…”

Influence of Salivary Macromolecules and Fluoride on Enamel Lesion Remineralization in vitro

“…This phenomenon can be partly explained by the inhibitory action of salivary macromolecules (mainly proteins) and pellicles on mineral deposition onto the tooth surface. Many studies have shown that salivary proteins strongly inhibit the induction and growth of hydroxyapatite; these proteins include statherin [Moreno et al, 1979;Hay et al, 1982Hay et al, , 1984, proline-rich proteins [Moreno et al, 1979;Aoba et al, 1984], histatins [Richardson et al, 1993], albumin [Robinson et al, 1992;Gilman and Hukins, 1994] and cystatins [Johnsson et al, 1991]. Furthermore, some proteins, such as albumin and mucins, have shown the ability to bind with calcium ions and are thought to be important constituents of acquired pellicles, which contribute substantially to the protective effect on acid demineralization [Arends et al, 1986;van Nieuw Amerongen et al, 1987].…”

Combined quantitative light-induced fluorescence (QLF™) and calcium assay for screening of remineralization potential of human saliva

“…With respect to caries formation and prevention, saliva has been studied by especially focusing on mineral saturation status and its relevant factors [1,2]. In contrast, salivary mineral contents were focused in this study and it was found that levels of salivary calcium and phosphate ions ranged extensively among individuals.…”