Biosynthesis and secretion of enamel proteins during hamster tooth development.

Experiments were designed to detect and determine the biosynthetic behavior of enamel proteins in Syrian Golden hamsters. Enamel matrix proteins were extracted from 3-day-old postnatal first molar tooth organs. Labeling pulse/chase experiments with [35S]-methionine followed by light microscopic autoradiography, or polyacrylamide slab gel electrophoresis and fluorography, showed the synthesis of epithelial-specific gene products. Synthesis and secretion of enamel proteins required approximately 30 min under these in vitro organ culture conditions; both enamelin and amelogenin proteins were synthesized and secreted into the forming extracellular matrix. Amelogenin proteins were secreted initially and rapidly degraded into increasingly smaller polypeptides. In contrast, enamelin proteins were secreted at a slower rate and remained more or less stable over the duration of the experiment. The specific activities of both classes of proteins increased over a 6-hour synthesis period, indicating the accumulation of both proteins into the forming extracellular matrix. Comparisons of the kinetics of formation and posttranslational processing of enamelin and amelogenin are consistent with the presence of possibly two different gene products in hamster secretory ameloblasts.