超好熱性古細菌Pyrobaculum islandicumのD-アミノ酸脱水素酵素とアラニンラセマーゼ

抄録

  Of archaea, methane-producing organisms do not possess D-enantiomers of amino acids. However, other archaea contain D-serine and D-aspartic acid. In order to confirm the presence of D-amino acids in archaea, we cultivated the hyperthermophile cells at 95℃, and searched for enzyme activities of D-amino acid production. Since a D-amino acid-dehydrogenase activity and an alanine-racemase activity were detected, we partially purified these enzymes. The optimum temperature of D-amino acid dehydrogenase was found to be 80℃, and the optimum pH was between 6.5 to 9.0. The enzyme activity was higher with D-proline as the substrate than with D-alanine. Alanine racemase activity was shown with both of the D- and L-alanine. In addition, the racemase showed some activity with L-serine, although the activity was less than 40% of that with L-alanine. The optimum temperature of the racemase was 40℃ with L-alanine as substrate, but no temperature dependency of the enzyme was observed with D-alanine.