Analysis of developing enamel of the rat. II. Electrophoretic and amino acid studies.

Amino-acid analyses showed that proline, glutamic acid and leucine were the most common amino acids in immature or developing enamel and in each of its fractions (i.e., in the 1st and 14th water-extractable fractions of a sequential series of extractions, EDTA-water soluble and water-insoluble fractions. The immature enamel and its 1st and 14th water-extractable fractions were similar in their proportions of the basic amino acids (lysine, histidine and arginine), the beta-hydroxylated aliphatic amino acids (valine, leucine, and isoleucine). On the other hand, the immature enamel differed from the water-extractable fractions chiefly in its relative content of aspartic acid, glutamic acid, alanine, proline, glycine, tyrosine and methionine. Also the 1st water-extractable fraction differed from the 14th in its amino-acid profile. tthe EDTA-water-soluble fraction most closely resembled the 14th water-extractable fraction except for its proportion of arginine and alanine residues. Although with polyacrylamide gel electrophoresis the EDTA-water-soluble and the water-extractable fractions exhibited companion bands (at least 7 peaks were evident at pH 9.3) they differed decidely as to which band was the most prominent. The water-insoluble fractions compared with any of the soluble fractions or with immature enamel showed a higher percent of serine, threonine, glycine, aspartic acid, alanine, valine, lysine, and arginine but relatively less glutamic acid, proline, methionine and histidine. Neither hydroxyproline nor hydroxylsine were detected in any of the samples.