Soluble and insoluble proteins of normal human mature enamel

Human mature enamel proteins were prepared by a combination of three extraction procedures in the presence or absence of de-aggregating agents before and after EDTA demineralization. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed the presence of a single low mol. wt protein in the water extract and multicomponent proteins with high mol. wt in the urea and urea-EDTA extracts. Polyacrylamide gel electrophoresis of the proteins contained in the three fractions after reduction and alkylation showed the existence of the two last fractions of different constitutive monomers linked by covalent and non-covalent bonds. Immunological comparison of the proteins showed at least one common protein in the E2 and E3 fractions. It is suggested that the high mol. wt proteins observed in mature enamel matrix were formed by combination of different monomers.