Protein-specific S-thiolation in human endothelial cells during oxidative stress

Cysteines of chloroplast NADP-malate dehydrogenase form mixed disulfides

Chloroplast NADP-malate dehydrogenase (NADP-MDH) from pea and from spinach was N-terminally truncated by limited proteolysis with Staphylococcus aureus protease V8. The resulting monomeric enzymes lacking, respectively, the 37 and 38 N-terminal amino acids were inactive. Reduction and addition of low concentrations of guanidine-HCl (50-100 mM) resulted in a highly active enzyme of 850 units per mg protein. Equilibration of the truncated enzyme with various glutathione (GSH) redox buffers and assaying its activity in the presence of guanidine-HCl was used to establish the existence of protein-GSH mixed disulfides. This finding was further confirmed using incorporation of radioactively labelled thiol. The possible function of such cysteine modifications under oxidative stress and their regeneration by the thioredoxin system in the light is discussed.

Thiol dependent oxidation of enzymes: the last chance against oxidative stress

1. A survey of known effects of oxidized thiols on enzyme activity reveals a potential concerted action on metabolic pathways determining an impairment of anabolic reduction processes and an activation of the oxidative arm of the hexose monophosphate shunt. Thus it appears that, following oxidative stress, the increase of disulphides may act in restoring a reduced state in the cell by specifically channelling the metabolic energy flux.

S-thiolation of human endothelial cell glyceraldehyde-3-phosphate dehydrogenase after hydrogen peroxide treatment

Exposure of human umbilical vein endothelial cells to oxidants such as hydrogen peroxide, tertbutyl hydroperoxide and diamide has been shown to induce oxidant-specific S-thiolation of cellular proteins. In this study one of the main S-thiolated proteins in hydrogen-peroxide-treated cells was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. Additionally, we have shown that the post-translational modification of the cysteinyl thiols of glyceraldehyde-3-phosphate dehydrogenase accompanies an inhibition of the enzyme and that both events are simultaneously and rapidly reversed upon the removal of the oxidative stimulus.

Sensory neuropeptide-mediated bronchoconstriction of the guinea pig lung by diamide; a comparison to hydrogen peroxide

The effect of the thiol oxidizing agent diamide on airway conductance, dynamic compliance and perfusion flow of isolated perfused and ventilated guinea pig lungs was investigated. When infused in the pulmonary circulation, diamide (100 microM) induced bronchoconstriction, but no effect on perfusion flow was observed. Although diamide exposure induced the formation of thromboxane A2, the thromboxane/prostaglandin endoperoxide receptor antagonist L-670,596 did not affect the decrease in conductance and compliance induced by diamide. Diamide induced the release of the sensory neuropeptide calcitonin gene-related peptide. The bronchoconstriction and the release of calcitonin gene-related peptide induced by diamide were abolished by capsaicin pretreatment of the guinea pigs. Combined pretreatment with the NK1 and NK2 receptor antagonists, CP-96,345 and SR-48968, attenuated the effect of diamide. Hydrogen peroxide-induced vaso- and bronchoconstriction was not affected by capsaicin-pretreatment, nor did hydrogen peroxide induce detectable release of calcitonin gene-related peptide. The results indicate that diamide activates sensory nerves and induces neuropeptide release and neurokinin receptor-mediated bronchoconstriction in the isolated perfused and ventilated guinea pig lung.

The S-thiolation of hepatocellular protein thiols during diquat metabolism

The effects of diquat metabolism on the protein thiol (PrSH) status of bis-chloronitrosourea-pretreated hepatocytes have been studied. Using a conventional, dithionitrobenzene-based assay for free PrSH in trichloroacetic acid-precipitated protein, control levels of PrSHs (83 +/- 6 nmol/mg protein) were unaltered during the initial 60 min of incubation of the cells with 1 mM diquat. However, using a radiochemical method for the determination of glutathionylation of PrSH [Grimm et al., Biochim Biophys Acta 844: 50-54, 1985], in which the hepatocytes were prepared from diethylmaleate-pretreated animals and reloaded with reduced glutathione (GSH) in the presence of [35S]methionine and cycloheximide, oxidation of hepatocellular PrSH by stimulated S-thiolation with GSH could be demonstrated. The S-glutathionylation of the protein was maximal after 30 min of treatment of the cells and preceded the onset of membrane leakage. However, the quantity of GSH mixed disulfide formed was limited to a maximum of 1.4 +/- 0.4 nmol GSH/mg protein, indicating the oxidation of only 2% of the total hepatocellular PrSH by S-thiolation. This percentage depletion is below the working variability of the colourimetric PrSH assay utilized and indicates strongly the use of the S-thiolation assay in the study of the possible effects of other redox-cycling cytotoxins on cellular PrSH status, as these may not be evident with conventional spectrophotometric techniques. The analysis of the cellular protein from diquat-treated cells by SDS-PAGE and autoradiography indicated the S-glutathionylation of a variety of cellular proteins, including species with molecular masses 17, 24, 26, 30, 40, 43 and 46 kDa. Although the identities of these species are uncertain (the 30-kDa protein may be equivalent to carbonic anhydrase as reported by Rokutan et al., Biochemistry 179: 233-239, 1989), it may be that oxidative modification of these proteins by stimulated S-glutathionylation may be an important early event in the mechanism of the hepatotoxicity of diquat.