Inhibition effect of thymoquinone and lycopene compounds on glutathione reductase enzyme activity purified from human erythrocytes.

Glutathione reductase (GR, EC 1.8.1.7) is a specific antioxidant enzyme that catalyzes oxidized glutathione (GSSG) to reduced glutathione (GSH). GR enzyme maintains the cellular reduced GSH level and plays a central role in cell defense against reactive oxygen species. Herein, GR was purified with affinity chromatography method in one step using 2',5'-ADP Sepharose 4B from human erythrocytes. The purification rate of glutathione reductase enzyme purified from human erythrocytes was 6224 fold and specific activity was calculated as 9.586 EU/mg protein. The molecular weight of GR was determined to be 53 kDa by SDS-PAGE. The effect of thymoquinone and lycopene compounds on the GR activity purified from human erythrocytes was researched. Both compounds showed an inhibitory effect on GR activity. IC50 values for thymoquinone and lycopene were calculated as 62.12 µM and 35.79 µM, respectively. Inhibition type and Ki values were determined from the Lineveawer-Burk graph. The type of inhibition for thymoquinone and lycopene was found to be non-competitive inhibition. Ki value was calculated as 57.71 µM for thymoquinone and 46.65 µM for lycopene. In this study, it was concluded that antioxidant compounds thymoquinone and lycopene, which have an inhibitory effect on GR activity, may have a therapeutic effect on cancer disease. Communicated by Ramaswamy H. Sarma.