IMMUNOCHEMICAL AND IMMUNOCYTOCHEMICAL STUDY OF A 15-KDA NON-AMELOGENIN AND RELATED PROTEINS IN THE PORCINE IMMATURE ENAMEL - PROPOSAL OF A NEW GROUP OF ENAMEL PROTEINS SHEATH PROTEINS

Our previous immunohistochemical study showed that in the porcine immature enamel, 13-17 kDa non-amelogenins were preferentially localized in the prism sheath. In this study, we revealed that the N-terminal amino acid sequence of a 15 kDa protein, one of the main components of the 13-17 kDa non-amelogenins, was VPAFPRQPGTHGVASL-, which shows no homology to those of known enamel proteins. In immunochemical analysis of porcine immature enamel, antibodies against a synthetic peptide containing this sequence reacted with many proteins of different molecular weights, especially with 62 kDa, 40 kDa and 10-19 kDa proteins. Of these proteins, the 62 kDa protein of the highest molecular weight was found only in newly formed enamel. In immunohistochemical preparations of the porcine tooth germs, the immunoreactivity of immature enamel just beneath the nonsecretory face of the Tomes' processes was intense. This immature enamel seemed to grow into the prism sheaths which showed intense immunoreactivity throughout the entire thickness of immature enamel at the matrix formation stage. The Golgi apparatus and secretory granules of the secretory ameloblasts showed immunoreactivity. These results suggest that the 62 kDa protein is a parent protein of the low molecular weight non-amelogenins. From its unique amino acid sequence and localization, we propose the low molecular weight non-amelogenins and their parent protein comprise a new family of enamel proteins designated as 'sheath proteins'.