TEMPORAL AND COMPOSITIONAL CHARACTERISTICS OF SALIVARY PROTEIN ADSORPTION TO HYDROXYAPATITE

Salivary proteins bind to enamel surfaces and hydroxyapatite in a high ly selective manner. Numerous studies have identified these proteins a s primarily proline-rich proteins, cystatins, statherin, and histatins . Previously, the hydroxyapatite-binding potential of these proteins h ad been characterized in systems consisting of singly purified protein and adsorbent. The purpose of this study was to investigate the adsor ption of each protein in the presence of complete salivary secretion. Proteins, shown to adsorb to hydroxyapatite, were purified, biotinylat ed, and added back to the remaining proteins to form a series of recon stituted secretions. The adsorption of each biotinylated protein in th e reconstituted secretion to hydroxyapatite was then measured as a fun ction of time. Results indicated that three different adsorption patte rns occur. A simple hyperbolic pattern is characteristic of amylase, g lycosylated proline-rich protein (PRG), and cystatin. A faster adsorpt ion process is observed for PRP-3, PRP-L PIF-f, and statherin. A more complex pattern, exhibiting a rapid phase followed by a slower phase, is characteristic of PRP-1, PRP-2, PIF-s, and histatins. These results suggest that there are different adsorption processes involved in the binding of salivary proteins to hydroxyapatite. Two possible mechanis ms are direct adsorption of protein to hydroxyapatite and indirect ads orption of protein by interacting with other proteins already bound to hydroxyapatite.