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

Abstract

γ-Glutamylcysteine (γ-EC) has antioxidant properties similar to those of glutathione (GSH) and acts as its precursor in mammals. There are a few procedures for the production of γ-EC, such as chemical synthesis or enzymatic synthesis from glutamate and cysteine; however, they are very costly and not suitable for industrial production. A phytochelatin synthase-like enzyme derived from Nostoc sp. Pasteur Culture Collection 7120 (NsPCS) catalyzes the hydrolysis of GSH to γ-EC and glycine in the absence of ATP or other additives. Our research aims to establish an alternative γ-EC production procedure with low cost and high productivity. To this end, we optimized the reaction conditions of NsPCS and characterized its properties in this study. We found that 200 mM potassium phosphate buffer, pH 8.0, at 37 °C, had the highest NsPCS activity among the conditions we tested. Under these conditions, NsPCS had a Km of 385 µM and a Vmax of 26 mol/min/mg-protein. In addition, NsPCS converted 100 mM GSH into γ-EC with high yields. These results suggest that the NsPCS reaction has great potential for the low-cost, industrial-scale production of γ-EC.