Abstract
Water-extractable alanine (EC 2.6.1.2) and aspartate aminotransferases (EC 2.6.1.1) in sound and carious human dentine were studied. Aspartate aminotransferase activity was higher than alanine aminotransferase activity in both sound and carious dentine. Both enzyme activities calculated per weight of the sample were higher in carious than in sound dentine. When the enzyme activities were calculated per mg protein in the sample, activities in sound dentine were higher than, or equal to, those observed with carious dentine, indicating that only non-structural proteins, such as many enzymes, were water-extractable from sound dentine. By DEAE-cellulose chromatography, one main enzyme peak representing aspartate aminotransferase activity was obtained from carious dentine. The activity of aspartate aminotransferase was high over 1 pH unit, the pH optimum being 7.4. This enzyme was stable for one hour at temperatures from +35 to +50 °C. The optimum temperature was +37 °C. Hg 2+ ions (2.0 mM), l(+)cysteine (2.0 mM) and dithiothreitol (0.2 mM) inhibited totally the enzymatic transamination of aspartate. These enzymes are believed to play a role in the degradation of excess amino acids in dentine during caries.
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