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.