l-Theanine Synthesis Using γ-Glutamyl Transpeptidase from Bacillus licheniformis ER-15

Recombinant γ-glutamyl transpeptidase (rBLGGT) from Bacillus licheniformis ER-15 was purified to homogeneity by ion-exchange chromatography. Molecular masses of large and small subunits were 42 and 22 kDa, respectively. The enzyme was optimally active at pH 9.0 and 60 °C and was alkali stable. Km and Vmax for γ-glutamyl-p-nitroanilide hydrochloride were 45 μM and 0.34 mM/min, respectively. l-Theanine synthesis was standardized using a one variable at a time approach followed by response surface methodology, which resulted in approximately 85–87% conversion of l-glutamine to l-theanine within 4 h. The standardized reaction contained 80 mM l-glutamine, 600 mM ethylamine, and 1.0 U/mL rBLGGTin 50 mM Tris-Cl (pH 9.0) at 37 °C. Similar conversions were also obtained with the enzyme immobilized in calcium alginate. Using immobilized enzyme, 35.2 g of l-theanine was obtained in three cycles of 1 L each. The product was purified by Dowex 50W X 8 hydrogen form resin and was confirmed by HPLC and proton NMR spectro...