Glutathione protein mixed disulfides

H22. Hitomi, M., Odani, S., and Ono, T., Glutathione-protein mixed disulfide decreases the affinity of rat liver fatty acid-binding protein for unsaturated fatty acid. Em J. Biochem. 187, 713-719 (1990). 

From such figures, it can be concluded that in normal in vivo conditions, proteins which are under thermodynamic control of the glutathione redox buffer should be predominantly in the PSH form when Reaction (32) is feasible, whereas they will be predominantly in the P(S)2 form when Reaction (33) is feasible. Formation of protein mixed-disulfides PSSG is therefore likely to be of greater importance than that of P(S)2 in situations of oxidative stress. In such conditions however, non-steady-state concentrations of GSH and GSSG will often prevail and protein activities will be primarily under control of kinetic constraints. 

B19. Brigelius, R., Muckel, C., Akerboom, T. P. M., and Sies, H., Identification and quantitation of glutathione in hepatic protein mixed disulfides and its relationship to glutathione disulfide. Biochem. Pharmacol. 32, 2529-2534 (1983). 

According to Lii and Hendrich 94), two pathways exist for the in vivo S-glutathiolation of protein SH groups (a) glutathione disulfide (GSSG)-protein mixed disulfide exchange (equation 4) and (b) direct combination of thiol free radicals to mixed disulfides, possibly as shown in equations 5-7. 

DeLucia, A. J., M. G. Mustafa, M. Z. Hussain, and C. E. Cross. Ozone interaction with rodent lung. III. Oxidation of reduced glutathione and formation of mixed disulfides between protein and nonprotein sulfhydryls. J. Gin. Invest. 55 794-802, 1975. 

As already discussed in chapter 4, reactive intermediates can react with reduced GSH either by a direct chemical reaction or by a GSH transferase-mediated reaction. If excessive, these reactions can deplete the cellular GSH. Also, reactive metabolites can oxidize GSH and other thiol groups such as those in proteins and thereby cause a change in thiol status. When the rate of oxidation of GSH exceeds the capacity of GSH reductase, then oxidized glutathione (GSSG) is actively transported out of the cell and thereby lost. Thus, reduced GSH may be removed reversibly by oxidation or formation of mixed disulfides with proteins and irreversibly by conjugation or loss of the oxidized form from the cell. Thus, after exposure of cells to quinones such as menadione, which cause oxidative stress, GSH conjugates, mixed disulfides, and GSSG are formed, all of which will reduce the cellular GSH level. 

Almost all cells contain a high concentration (3-9 mM) of the thiol-containing tripeptide glutathione (G-SH, Box 11-B). In its disulfide form it participates in forming disulfide bridges in secreted extracellular proteins (Eq. 10-9) via intermediate mixed disulfides. Mixed disulfides with glutathione as well as with other thiols can also be formed within cells by oxidative... 

However, the two proteins have significantly different specificities and functions. The disulfide loop in glutaredoxin, whose eukaryotic forms are often called thioltransferases/ has the sequence CPYC. Although glutaredoxins are weaker reductants of mixed disulfides of proteins with glutathione than are thioredoxins/1 sthey are more specific. 

Studies with [35S]- and [14C]-captopril have indicated complex and extensive metabolism. The disulfide dimer of captopril is observed, as well as mixed disulfides with cysteine, N-acctylcysteine, and glutathione. There is covalent reversible binding to plasma proteins, which is similarly considered to involve disulfide linkages. S-Methylcaptopril and its sulfoxide are also formed (105). 

A large number of enzyme activities have been shown to be affected by protein S-thiolation with glutathione redox buffers in vitro (reviewed in ref. [271]). Extracellular and cell-surface proteins are commonly activated by the formation of intramolecular disulfides. Conversely, most of the responsive intracellular enzymes are down-regulated by the formation of mixed disulfides, with the interesting exception of enzymes involved in the delivery of free glucose. 

R3. Raghavachari, N., Qiao, F., and Lou, M. F., Does glutathione-S-transferase dethiolate lens protein-thiol mixed disulfides A comparative study with thioltransferase. Exp. Eye Res. 68, 715-724 (1999). 

Bass R, Ruddock LW, Klappa P, Freedman RB. A major fraction of endoplasmic reticulum-located glutathione is present as mixed disulfides with protein. J. Biol. Chem. 2004 279 5257-5262. 

Figure 2. The incubation in the presence of GSSG induces the S-glutathionylation of c-Jun and an inhibition in its DNA binding activity. A) The DNA binding of c-Jun was subjected to EMSA experiments in the presence of different GSH/GSSG ratios or DTT. B) In the figure is represented the amount of c-Jun protein which is modified to mixed disulfide with glutathione (P-S-S-G) or to other modifications.

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