Optimization of Reaction Conditions for γ-Glutamylcysteine Production from Glutathione Using a Phytochelatin Synthase-Like Enzyme from Nostoc sp. Pasteur Culture Collection 7120

Effective Repeated Production of γ-glutamylcysteine, Essential For Intracellular Glutathione Production, Using Cellulose-immobilized Phytochelatin Synthase-like Enzyme NsPCS

γ-Glutamylcysteine (γ-EC) can increase intracellular glutathione (GSH) levels, which may prevent and alleviate age-related disorders and chronic diseases caused by oxidative damage. However, the commercial availability of γ-EC remains limited owing to its complex chemical synthesis from glutamate and cysteine. In this study, we have developed the method of the effective conversion of GSH to γ-EC to achieve the optimal reaction conditions for repeated batch production and potential application in industrial γ-EC production using the phytochelatin synthase-like enzyme NsPCS. For repeated batch conversion reactions, the optimal temperature was determined at 25 °C, where γ-EC showed good stability compared with that at 37 °C, leading to higher overall productivity. Cellulose sponges and microcrystalline cellulose (MCC) showed superior mechanical strength as immobilization carriers and greater stability and productivity than other materials. The total amounts of γ-EC obtained by NsPCS immobilized on the cellulose sponge and MCC were 305 mg and 291 mg, respectively, in a 5 mL reaction over five repeated batch reactions. These simple production processes are easily reproduced, and their high volumetric efficiency is promising for the industrial production of stable and low-cost γ-EC.

Reactivity of γ-glutamyl-cysteine with intracellular and extracellular glutathione metabolic enzymes

Gamma-glutamyl-cysteine (γ-EC) is a precursor of glutathione (GSH) biosynthesis. We investigated whether it functions as a substrate for three intracellular and one extracellular GSH metabolic enzymes, which mediate the antioxidant defence function of GSH. Among them, glutathione peroxidase, glutathione S-transferase and γ-glutamyl transferase (GGT) exhibited substrate specificity for γ-EC, whereas glutathione reductase did not. The specificities of γ-EC and its disulphide form to GGT were comparable to GSH and its oxidized form, GSSG respectively. These results indicate that they can supply GSH constituent amino acids, glutamate, cysteine and cystine through degradation by GGT. γ-EC may contribute valuable antioxidant defence properties as a food and cosmetic additive.