Inhibitory effect of ascorbic acid on glutathione S-transferase from human erythrocytes

Inhibition of certain specific glutathione S-transferase isozymes is associated with the efficacy of chemotherapy in the treatment of cancer patients. We aimed to determine whether ascorbic acid, which can be used as a drug and antioxidant food supplement, is a glutathione S-transferase isozyme inhibitor. For this purpose, glutathione S-transferase was first purified from human erythrocytes and the in vitro effect of ascorbic acid on enzyme activity was investigated. Then, kinetic studies were performed to evaluate the inhibition potential of ascorbic acid, which was determined to be an inhibitor of the enzyme. The enzyme was purified 1286-fold with a yield of 81% and specific activity of 18.00 U/mg protein. The effects of ascorbic acid were tested on the in vitro enzyme activity of glutathione S-transferase and detected to be an inhibitor for the enzyme with 10 mM of IC50 value. Ki constants and inhibition type were also determined for the enzyme. This finding indicates that ascorbic acid can be an effective inhibitor of some GST isoenzymes increased in cancer cells. Abundant ascorbic acid intake may prevent cancer formation by strengthening the antioxidant defense system, on the other hand, it may increase the effectiveness of cancer treatment by inhibiting the chemotherapy-resistant GST enzyme.