Electron-microscopical studies of conformational changes in dentinal phosphophoryn.

p67tinal phosphophoryn was isolated and purified from unerupted calves molars by the methods of Butler et al. (1981). The resulting proteins were concurrently analyzed by circular dichroism and electron microscopy after low-angle rotary shadowing. Electron microscopy of these proteins in aqueous solutions revealed extended bead-like chains that possessed intramolecular variations in morphology. The addition of calcium ion or methanol to solutions of these proteins produced circular dichroism spectra indicative of more ordered structures. Electron microscopy of these preparations revealed aggregates of 25-30 nm disc-like structures. Although correlations of domain sequences and structure were not possible, the resulting structures did possess molecular morphologies that are compatible with some of the functional roles advocated for these proteins as calcium hydroxyapatite nucleating sites in the mineralization of dentin (Lechner et al., 1981).