The amino acid composition of the organic matrix and the neutral-soluble and acid-soluble components of embryonic bovine enamel.

The proteins of developing dental enamel matrix, although among the least studied of all the extracellular proteins, have nevertheless been found to possess certain unique and interesting properties. The amino acid composition has been characterized by the highest content of proline thus far reported for any protein (approx. 200-250 residues/1000 amino acid residues), a relatively large number of glutamic acid and histidine residues, and the presence of hydroxyproline and hydroxylysine (Eastoe, 1960, 1963; Glimcher, Mechanic, Bonar & Daniel, 1961 a; Piez, 1961). Except for collagen and polyproline, the configurations proposed for fibrous proteins cannot accommodate such large amounts of proline (Lindley, 1955; Szent-Gyorgyi & Cohen, 1957; Glimcher et al. 1961 a). By constructing models a possible configuration was found which permitted as many as 250 residues of proline/1000 amino acid residues to be randomly incorporated into the polypeptide chains (Glimcher et al. 1961 a). The structure proposed was composed of anti-parallel pleated sheets with a 1800 bend of the polypeptide chains for each proline residue and was similar to the cross: configuration suggested by Astbury, Beighton & Parker (1959). Cross-. X-ray-diffraction patterns have been obtained from histologically identified embryonic bovine enamel matrix that had the characteristic amino acid composition (Glimcher, Bonar & Daniel, 1961 b). Further characterization of the proteins has been hampered by the extremely limited amount oftissue available and the relative insolubility of the proteins (Eastoe, 1963). In the present study, most of the proteins of the decalcified organic matrix of developing bovine tooth enamel were found to be soluble in cold neutral buffer solution of low ionic strength, and the residue remaining after exhaustive neutral-buffer extraction dissolved in mild acid. The amino acid composition of these fractions was investigated.