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 imma ture enamel, 13-17 kDa non-amelogenins were preferentially localized i n the prism sheath. In this study, we revealed that the N-terminal ami no acid sequence of a 15 kDa protein, one of the main components of th e 13-17 kDa non-amelogenins, was VPAFPRQPGTHGVASL-, which shows no hom ology to those of known enamel proteins. In immunochemical analysis of porcine immature enamel, antibodies against a synthetic peptide conta ining this sequence reacted with many proteins of different molecular weights, especially with 62 kDa, 40 kDa and 10-19 kDa proteins. Of the se proteins, the 62 kDa protein of the highest molecular weight was fo und only in newly formed enamel. In immunohistochemical preparations o f the porcine tooth germs, the immunoreactivity of immature enamel jus t beneath the nonsecretory face of the Tomes' processes was intense. T his 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 secretor y granules of the secretory ameloblasts showed immunoreactivity. These results suggest that the 62 kDa protein is a parent protein of the lo w molecular weight non-amelogenins. From its unique amino acid sequenc e and localization, we propose the low molecular weight non-amelogenin s and their parent protein comprise a new family of enamel proteins de signated as 'sheath proteins'.