Localization of enamel proteins : an electron microscopic immunocytochemical study using antibodies against synthetic peptides.

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Immature enamel of the pig and the rat were investigated immunochemically and immunocytochemically using antibodies against synthetic peptide fragments of porcine enamel proteins. The results are summarized as follows.1. Originally secreted amelogenin, the 25 kDa amelogenin, is preferentially localized in the surface layer of immature enamel and is degraded to produce 20 kDa and other lower molecular weigh amelogenins which are found in deeper layer of the immature enamel.2. The 6-7 kDa amelogenin ( N-terminal segment containing residues 1-45 of the 25 kDa amelogenin) produced by degradation of the 20 kDa amelogenins were rarely found in surface layer and were predominantly localized in deep layer, especially in the rod sheath of immature enamel.3. The 89 kDa enamelin is localized in rod and interrod enamel just after its secretion from the ameloblast and is degraded faster than the 25 kDa amelogenin. Some N-terminal low molecular weight peptides produced by degradation of the 89 kDa enamelin may be concentrated in the rod sheaths.4. The rod sheaths are primarily composed of a new category of enamel protein family, the rod sheath proteins, different from the amelogenins or enamelins. Degraded amelogenins and enamelins are then added to the rod sheaths. Molecular weights of originally secreted rod sheath proteins are estimated 30-40 kDa and may be degraded faster than the 25 kDa amelogenin.5. The rod sheaths are absent from the immature enamel of rat incisors and molars, indicating the amelogenesis of the rat may somewhat differ from that of pig and man.6. The 32 kDa nonamelogenin protein is likely to be a degradation product of the 140 kDa and/or 89 kDa proteins, both of which are present in the rod and interrod enamel and may play a significant role in the initial calcification and crystal growth regulation in the amelogenesis.