Feasibility of synthesizing γ-[Glu]_(n≥1)-Gln using high solid concentrations and glutaminase from Bacillus...

Effects of using high solid concentrations on the synthesis of γ-[Glu]_(n≥1)-Gln catalyzed by glutaminase from Bacillus amyloliquefaciens were examined in this study. An increment in solid concentration from 10% to 50% (w/w) increased the extent of synthesis of γ-[Glu]_(n≥1)-Gln, based on the analyses of amino acid composition and amino nitrogen content. Size-exclusion high-performance liquid chromatography analysis revealed an increase in molecular mass of γ-[Glu]_(n≥1)-Gln resulting from the increase of solid concentration from 10% to 50% (w/w). UPLC-Q-TOF-MS/MS analysis showed that the enzymatic reaction mixtures post γ-glutamyl transpeptidation contained γ-Glu-Gln, γ-Glu-Glu-Gln, γ-Glu-Glu-Glu-Gln, γ-Glu-Glu-Glu-Glu-Gln and γ-Glu-Glu-Glu-Glu-Glu-Gln. The intensity of each γ-[Glu]_{(n=1,2,3,4,5)}-Gln produced at a solid concentration of 50% (w/w) was higher than that at 10% (w/w). These findings indicated the potential of such an energy- and water-efficient approach for synthesizing γ-[Glu]_(n≥1)-Gln at high solid concentrations.