The free amino acids in human dental plaque

Analysis of plaques from maxillary and mandibular incisors for free amino acids showed that the dicarboxylic amino acids, glutamic and aspartic, were present in largest amounts, with glutamic acid comprising at least 50 per cent of the total pool. Other amino acids in decreasing order of prominence included proline, ornithine, alanine, lysine, glycine, threonine and serine. This pattern was basically the same in the plaques from the different incisor sites but was clearly different from those of hydrolysates of either the plaque bacteria or the plaque matrix. The results were consistent with the most prominent plaque-free amino acids being associated mainly with the intermediary metabolism of the plaque bacteria. Urea and glucose were then applied to plaque in vivo in the form of rinses to determine if during their metabolism any of the plaque amino acids are affected. Glutamic- and aspartic-acid concentrations both rose after plaque exposure to urea accompanied by a small rise in alanine. After glucose exposure, aspartic- and glutamic-acid concentrations both showed large decreases and alanine showed a small increase. With glucose plus urea, glutamic acid rose and fell, aspartic acid decreased slightly and alanine increased several fold. In each case, the other free amino acids showed little or no change. Thus glutamic and aspartic acids are major components of the intra-cellular pool of amino acids and probably play an important role in alanine synthesis, presumably by facilitating transamination of pyruvate.