Some Properties of a Monomeric Alanine Racemase from an Extreme Thermophile, Thermus thermophilus
Teck Keong SEOW*, Kenji INAGAKI, Takeshi NAKAMURA, Ritsuko MAEDA, Takashi TAMURA, and Hidehiko TANAKA
Department of Bioresources Chemistry, Okayama University, Faculty of Agriculture, 1-1-1 Tsushima-Naka, Okayama-Shi, Okayama 700, Japan
Alanine racemase (EC 5.1.1.1) catalyses the racemization of D- and L-alanine and is indispensable in the synthesis of the peptidoglycan layer through the supply of D-alanine. The enzyme is ubiquitous and has been isolated from various bacteria, including the moderate thermophile, Bacillus stearothermophilus. However, there had been no reports of the enzyme from extreme thermophilic bacteria. We have been able to isolate and purify the alanine racemase from Thermus thermophilus HB8. Further studies on the characteristics of the alanine racemase demonstrated that the enzyme is most active at pH 8 and showed no loss of activity even after incubation at 80℃ for 30 min. We also found that the enzyme possesses a monomeric structure with a molecular weight of about 38,000. As there are few reports of monomeric alanine racemases, we believe that the enzyme fromThermus thermophilus HB8 will be an interesting model for studies to unravel the reaction mechanism of alanine racemases.
