Glutathione oxidation-reduction potential

Many, but not all, proteins are sensitive to alterations in the oxidation-reduction potential of their environment. The effect is caused in part by oxidation of sulfhydryl groups or reduction of disulfide bonds. Not all proteins are equally sensitive to such alterations, but when they are, it is critical to be aware of their sensitivity. The purification or assay of some proteins can be accomplished only by providing reducing conditions (reduced glutathione, free cysteine, dithiothreitol, or mercap-toethanol) in all buffer solutions. 

E. S. Barron Ascorbic acid cannot protect the oxidation of glutathione because its oxidation-reduction potential is much more positive than that of glutathione. 

This reaction would not be expected to be reversible since the oxidation-reduction potential of ascorbate is more positive than that of GSH. Plants contain ascorbic acid reductase an enzyme which catalyzes the above reaction (109, 110), while animal tissues do not possess this enzyme. The nonenzymic oxidation of GSH by dehydroascorbate is sufficiently rapid however to be of biological significance and could under certain conditions act as an oxidizing system of TPNH via glutathione reductase. 

This thiol-disulfide interconversion is a key part of numerous biological processes. WeTJ see in Chapter 26, for instance, that disulfide formation is involved in defining the structure and three-dimensional conformations of proteins, where disulfide "bridges" often form cross-links between q steine amino acid units in the protein chains. Disulfide formation is also involved in the process by which cells protect themselves from oxidative degradation. A cellular component called glutathione removes potentially harmful oxidants and is itself oxidized to glutathione disulfide in the process. Reduction back to the thiol requires the coenzyme flavin adenine dinucleotide (reduced), abbreviated FADH2. 

---