Direct spectroelectrochemical titration of glutathione

Previous potentiometric attempts to determine the formal potential (E′0) of key intracellular redox buffer glutathione resulted in contradictory values. We have developed a spectroelectrochemical method using direct reduction on metal oxide electrodes. Disulfide absorbance at 258 nm was used to titrate glutathione in the thin layer cell reversibly. At conditions close to physiological ([GSH]=0.001–0.005 mol/l, pH=7.34; I=0.1 mol/l; T=298.15 K), we have measured glutathione E0′=−0.22±0.02 V (NHE), corroborating the results of equilibrium measurements.