Abstract: The purpose of this study was to investigate the effect of 732 cation-exchange resins on the activity of glutamate decarboxylase (GAD, EC4.1.1.15) in Enterococcus faecium and to establish a novel 732 cation-exchange resin-E. faecium cell suspension complex system for the biotransformation of L-glutamic acid (L-Glu) to γ-aminobutyric acid (GABA). The results indicated that 732 cation-exchange resins fully equilibrated in 0.2 mol/L sodium acetate buffer (pH 4.2) containing 0.2 mol/L L-Glu could significantly enhance the GAD biotransformation activity of E. faecium cells, increasing the yield of GABA by 32.30% as compared to the control group. A solid mixture of L-Glu and MSG (monosodium glutamate) (2:1) also could significantly improve GABA production by effectively regulating the pH value and maintaining the substrate concentration in the reaction solution. When the addition amount of the solid mixture was 30 g/L, the yield of GABA was improved by 52.40% as compared to that obtained without the addition of the mixture. Moreover, 732 cation-exchange resins and L-Glu/MSG (2:1) solid mixture could synergistically enhance the biotransformation activity of GAD in the cells. The optimal system was composed of 10 g of 732 cation-exchange resins, 10 mL of 0.2 mol/L sodium acetate solution containing 0.3 mol/L MSG (pH 4.2), 10 mL of 100 mg/mL E. faecium cell suspension and 30 g/L of L-Glu/MSG (2:1) solid mixture. When the system was incubated at 40 ℃ in water bath oscillator at 80 r/min, the yield of GABA was (4.57 ± 0.11) mmol, which was improved by 99.56% as compare to that ((2.29 ± 0.08) mmol) of the control group.

Key words: Enterococcus faecium, glutamate decarboxylase, 732 cation-exchange resin, gamma-aminobutyric acid, biotransformation activity