Electrophoretic and immunological characterization of the acquired enamel pellicle

Abstract

The acquired enamel pellicle, the in vivo pellicle, is a thin protein layer that arises from the adsorption of salivary proteins onto the enamel surface of teeth. One of its roles is to maintain the integrity of the tooth surface by affecting both demineralization and remineralization processes. In addition, the acquired enamel pellicle is the substrate on which initial bacterial colonization takes place, a process which depends upon the nature of the pellicle. ln this study, the two hour in vivo formed enamel pellicle was characterized and compared to the two hour in vitro formed pellicle derived from pure parotid secretion. Amino acid analysis, high sensitivity SDS p01yacrylamide gel electrophoresis, both anionic and cationic polyacrylamide gel electrophoresis and Western blot analysis were used to study the composition of in vivo pellicle. The antibodies for Western blot analysis were selected based upon in vitro studies demonstrating the affinity of certain salivary proteins to hydroxyapatite. Since the amino acid composition of acquired enamel pellicle is different from those of parotid and submandibular secretions, the pe11icle is composed of selectively adsorbed proteins. Based on the electrophoretic results from Tricine buffered, highly crosslinked, polyacrylamide gels, the acquired enamel pel1icle contains approximately 25 proteins or peptides ranging in apparent molecular weightS from 200 kDa to 7 kDa. This is surprising since in vitro models using salivary secretions contain approximately five components on these gels. It is also interesting to note that of the proteins tested by Western blot analysis, only one, amylase, was clearly detected. Proline-rich proteins, statherin, and histatins readily identified in in vitro pellicles were below the levels of detection in the in vivo formed pel1icle. These results suggest that the in vivo enamel pellicle is composed of some proteins from salivary secretions in their intact form and other proteins which may be proteolytically degraded salivary proteins, complexes of salivary proteins, or proteins of nonsalivary origin.