Ethylenediaminetetraacetic Acid Insoluble Protein of Adult Human Enamel

Abstract

Adult human normal enamel was extracted with EDTA under dissociative conditions, giving a soluble protein fraction and an insoluble residue. This residue, .apprx. 10-20% of the original sample mass, contained enamel hydroxylapatite associated with small amounts of matrix protein. The latter only became released after dissolution in lactic acid. The EDTA-soluble and the lactic acid-soluble adult enamel proteins were glycoproteins small in size (2000-3000 daltons on dissociative gel filtration chromatography) and similar in amino acid composition. These 2 protein fractions did differ significantly in their organic P contents, the lactic acid-soluble protein containing higher levels of this substituent. The EDTA dissolution resistance of the hydroxylapatite crystals contained in this insoluble residue possibly resulted from a strong association of the enamel apatite with the phosphorylated adult enamel matrix glycoprotein constituent.