Degradation of enamelins by proteinases found in porcine secretory enamel in vitro.

The action of proteinases obtained from porcine secretory enamel on the porcine 89-kDa enamelin was examined in vitro. The results of sodium dodecyl sulphate-acrylamide gel electrophoresis of the reaction products indicated the following. (1) The 76- and 78-kDa proteinases localized in the outermost layer of the secretory enamel not only convert the 25-kDa amelogenin to the 20-kDa amelogenin, but also split the 89-kDa enamelin, which is the major enamelin component in the enamel in the very early secretory stage, into large fragments such as 25-, 41- and 56-kDa enamelins. (2) The serine proteinases localized in the inner layer of secretory enamel further degrade not only amelogenins but also enamelins.