The amino acid composition of the organic matrix of decalcified fetal bovine dental enamel.

The organic matrix of dental enamel is produced by morphologically characteristic cells of the enamel organ (ameloblasts), which are derived from the stratified epithelial cells of the primitive oral cavity (1). On the basis of its ectodermal origin, as well as its chemical composition, physical properties, and histochemical staining characteristics, the protein component of the organic matrix, which accounts for the bulk of the organic material, has been classified as a eukeratin (2-6). Reports of the amino acid composition of the total enamel protein, as well as soluble and insoluble fractions, have varied considerably (2-S). The discrepancies seem to stem primarily from the difficulty of isolating sufficient quantities of enamel protein free from the underlying dentin which contains approximately 40-fold more protein, principally collagen, than fully calcified enamel, and from surface protein “cuticles” (either remnants of the enamel organ or films deposited from saliva). Previous work from this laboratory has shown that it is possible to separate cell-free ethylenediaminetetraacetate-decalcified enamel matrix from both the cellular enamel organ and the underlying dentinal collagen of fetal unerupted bovine incisor teeth at certain ages of the fetus (9). Furthermore, both the histological structure of the matrix and its molecular configuration as determined by x-ray diffraction are preserved (9). It was thought that an amino acid analysis of the cell-free organic matrix of enamel which had been histologically, histochemically, and crystallographically characterized would prove of value, since this has not been accomplished in the past. The x-ray diffraction studies previously mentioned (9) revealed that the protein was in the cross-p configuration. Except for the suggested cross-p configuration of actomyosin films after treatment with adenosine triphosphate (lo), the enamel protein is the only naturally occurring vertebrate protein thus far reported to be in this particular molecular configuration. The only other naturally occurring cross-p proteins are the silk-like protein of the chrysopa egg stalk (11) and the protein of bacterial flagella (12). Since the nature of the polypeptide chain configuration responsible for the cross-0 diffraction pattern is still under investigation (11, 13-15), it was felt that a complete amino acid analysis of a naturally occurring protein which had this