초록
l-Theanine, which has seen increasing use in the functional food industry, can be prepared via enzymatic synthesis using γ-glutamyltranspeptidase (GGT; EC 2.3.2.2). In this study, the GGT from Bacillus subtilis 168 was cloned and expressed as a secreted protein using Escherichia coli BL21(DE3). The enzymatic properties of the GGT and the optimal conditions for the enzymatic synthesis of l-theanine were investigated in detail. The activity of the enzyme was optimal at pH 10; the optimal temperature was 50<SUP>o</SUP>C. Desirable pH stability was observed between pH 5 and pH 12, and adequate thermostability was seen at 50<SUP>o</SUP>C. In 5h at 37<SUP>o</SUP>C, the enzyme converted 200mM l-glutamine and 2.2M ethylamine to l-theanine with a final yield of 78%. Yields of l-theanine decreased to 58% when using 500mM Gln and 45% when using 1M Gln. The yield of l-theanine obtained at high substrate concentration provides the basis for the industrial-scale production of l-theanine.