Enamel matrix: structural proteins.

Cell-free, fetal bovine enamel tissue was examined intact by high resolution. 13C Fourier transform, nuclear magnetic resonance spectroscopy. Two types of protein chains were observed under these conditions, one exhibiting rapid mobility and accounting for approximately two-thirds of the enamel matrix, while the other exhibited restricted or anisotropic segmental motion and accounted for the remaining third of the matrix. Sequential extraction of this fetal enamel under non-degradative conditions with dissociative solvents yielded two biochemically distinct populations of matrix protein. As expected, the bulk of the matrix consisted of proline-rich amelogenins, although the SDS-gel electrophoresis molecular weights for these proteins were somewhat higher than those reported using other extraction methods. Approximately fifteen percent of the total matrix consisted of much higher molecular weight phosphoproteins (46,000-72,000 daltons) whose amino acid composition closely resembled that reported for mature enamel protein. These high molecular weight proteins were tightly bound to the fetal enamel apatite crystallites.