EDTA soluble protein of human mature normal enamel.

Pure human mature enamel was prepared using a careful microdissection technique. After EDTA dissolution, the soluble proteins were recovered representing a concentration of 0.035% in the initial enamel. When the samples were analyzed with polyacrylamide gel electrophoresis, Coomassie Brilliant Blue staining revealed only one sharp fast migrating band, whereas o-toluidine blue, methylene blue, Amido Black 10B, and pyronine red G showed a thin double band at the same migration distance. Ultracentrifugation studies suggested that the proteins were of low molecular weight or of weak density. Absorption spectra showed a strong absorbance at 260 nm. After hydrolysis, amino acid analyses yielded a composition of 25% Gly, 13.5% Glu, 11% Ser, and 11% Pro. Cysteine measured as cysteic acid was present at 2%, and 2% hydroxyproline was found. A carbohydrate content of 15% was estimated by the anthrone method. Glucose, galactose, mannose, and fucose, identified through gas chromatography, were in a molar ratio of 9:4:3:1. Thus the organic matrix of adult human enamel consists of one or possibly two acidic glycoproteins.