Inhibitory Effect of Glutathione on the Generation of Hydroxyl Radicals in the Reaction System of Glutathione-Alloxan

Abstract

Deoxyribose (DOR) degradation, an indicator of hydroxyl radical (OH·) generation, was observed in the reaction system of glutathione (GSH)-alloxan in the presence of Fe³⁺-ethylenediaminetetraacetic acid (EDTA). GSH had a biphasic action on the DOR degradation, i.e. GSH at low concentrations caused marked activation and at high concentrations had an inhibitory effect. GSH at high concentrations had an ability to scavenge OH· in the hypoxanthin-xanthine oxidase in the presence of Fe³⁺-EDTA and to inhibit the oxygen consumption and the generation of the alloxan radical (AH·) and superoxide anion radical in the GSH-alloxan system. At GSH : alloxan ratio of 10 : 1 led to an immediate formation of dialuric acid. The autoxidation of dialuric acid was suppressed by GSH in a concentration-dependent fashion. These results indicate that autoxidation of dialuric acid is strongly suppressed by excess GSH in the alloxan-dialuric acid redox cycle, resulting in the decrease of AH·generation and oxygen consumption.On the other hand, the reduction of Fe³⁺-EDTA to Fe²⁺-EDTA by dialuric acid and AH· was scarcely inhibited by any concentrations of GSH. These results indicate that adding an excess of GSH suppresses the generation of OH· in the GSH-alloxan system through the inhibition of the redox cycling reaction between alloxan and dialuric acid independently on the reduction of Fe³⁺-EDTA to Fe²⁺-EDTA.