Increasing antioxidant activities of the glutamine-cysteine mixture by the glutaminase from Bacillus amyloliquefaciens.

In this study, we found that glutaminase from Bacillus amyloliquefaciens could increase antioxidant activities of Gln-Cys mixture, demonstrated by the higher superoxide anion and DPPH radical scavenging activities, Fe-chelating and reducing power. According to UPLC-Q-TOF-MS/MS results, we identified γ-[Glu]-Cys in Gln-Cys mixture in the presence of glutaminase. The yields of γ-Glu-Cys (GC) and γ-Glu-γ-Glu-Cys (GGC) were 40.92% and 22.79% respectively, under the established optimum conditions: pH 10, 37 °C, 3 h, 0.1 mol/l Gln: 0.1 mol/l Cys = 1:1, and glutaminase at 0.1% (m/v). The antioxidant properties of GC, GGC, glutathione and Gln-Cys mixture in the presence of glutaminase were further compared and we found GC exhibited the highest superoxide anion and DPPH radical scavenging activities, and Fe-chelating and reducing power. Therefore, glutaminase caused the increase of antioxidant activity of Gln-Cys mixture and might be attributed to GC which was synthesized by glutaminase via transpeptidation, and GC has the potential to be used in food and nutraceutical applications as an antioxidant peptide.