ENAMELYSIN (MATRIX METALLOPROTEINASE-20) - LOCALIZATION IN THE DEVELOPING TOOTH AND EFFECTS OF PH AND CALCIUM ON AMELOGENIN HYDROLYSIS

The formation of dental Enamel is a precisely regulated and dynamic de velopmental process. The forming enamel starts as a soft, protein-rich tissue and ends as a hard tissue that is over 95% mineral by weight. intact amelogenin and its proteolytic cleavage products are the most a bundant proteins present within the developing enamel. Proteinases are also present within the enamel matrix and are thought to help regulat e enamel development and to expedite the removal of proteins prior to enamel maturation. Recently, a novel matrix metalloproteinase named en amelysin was cloned from the porcine enamel organ. Enamelysin transcri pts have previously been observed in the enamel organ and dental papil lae of the developing tooth. Here, we show that the sources of the ena melysin transcripts are the ameloblasts of the enamel organ and the od ontoblasts of the dental papilla. Furthermore, we show that enamelysin is present within the forming enamel and that it is transported in se cretory vesicles prior to its secretion from the ameloblasts. We also characterize the ability of recombinant enamelysin (rMMP-20) to degrad e amelogenin under conditions of various pHs and calcium ion concentra tions. Enamelysin displayed the greatest activity at neutral pH (7.2) and high calcium ion concentration (10 mM). During the initial stages of enamel formation, the enamel matrix maintains a neutral pH of betwe en 7.0 and 7.4. Thus, enamelysin may play a role in enamel and dentin formation by cleaving proteins that are also present during these init ial developmental stages.