Investigation on enzymatic synthesis of 1-theanine with Zinc(II)-L-glutamine complex and its mechanism

To restrain the side reaction of autotranspeptidation, the complex of L-glutamine-Zn(II) [Zn(Gln) ₂] was prepared and used for enzymatic synthesis of theanine via γ-glutamyltranspeptidation (GGT) reaction. The stability and reactivity of Zn(Gln) ₂ were satisfactory under the reaction conditions. Moreover, autotranspeptidation was restrained effectively when Zn(Gln) ₂ instead of L-glutamine (Gln) was used as the γ-glutamyl donor. The kinetic parameter K _m of B. subtillus GGT toward Zn(Gln) ₂ and Gln was calculated to be 0.53 and 1.01 mmol/L respectively. Under the conditions of 6 mmol/L Zn(Gln) ₂, 200 mmol/L ethylamine, and 0.5 mmol/mL GGT, 7.38 mmol/L of theanine was obtained after incubation at 37°C for 2 h, indicating an increase of 14.42% compared with that using Gln as the donor substrate.