Sulphydryl radical

The reaction of oxyhaemoglobin with phenylhydrazine was studied in whole blood samples (Maples et al., 1988). Hydrazine-based drugs induce destruction of red blood cells with resulting haemolytic anaemia. Using DMPO as a trap, nitroxide radicals were detected, but these had solid-state or immobilized spectra with broad parallel and perpendicular features. Whilst no firm identification is possibly based on ESR spectra, except that the trapped radical must be a high polymer, various lines of evidence lead to the conclusion that the adduct was formed from a sulphydryl radical on oxyhaemoglobin. Chloroform extracts gave the phenyl radical adduct in accord with in vitro studies. 

Mass Spectra. The mass spectra of aromatic sulphines, aryl arylthio sulphines, aryl arylsulphinyl sulphines and aryl arylsulphonyl sulphines have been interpreted. In all cases the occurrence of a rearrangement involving the intermediacy of an oxathiiran could be established. The loss of a sulphydryl radical from the molecular ion appeared to be a characteristic process by the electron-induced fragmentation of thioamides, and this was in some cases taken as evidence for pronounced enethiolization of the molecular ion. The fragmentation... 

Dabrowski, A. and Chwiecko, M. (1990). Oxygen radicals mediate depletion of pancreatic sulphydryl compounds in rats with caerulein-induced acute pancreatitis. Digestion 7, 15-19. 

Oxidation of enzyme sulphydryl groups by free radicals (Armstrong and Buchanan, 1978) and by the longer lived chloroamines (Weiss et al., 1983), contributes to enzymic dysfunction and to the decrease in serum sulphydryl levels, primarily mercaptoalbumin, found in coalworkers with rheumatoid inflammatory disease (Thomas and Evans, 1975). Formation of the S-nitroso adduct of plasma mercaptalbumin is thought to provide a metastable reservoir for intravascular nitric oxide release (Stamler etal., 1992). 

A major contribution of the free-radical scavenging activity in blood plasma is attributable to the macro-molecular proteins (Wayner et al., 1985) of which albumin is a primary component and trapping agertt (Holt et al., 1984). Serum sulphydryl levels, primarily albumin-related, are decreased in subjects with rheumatoid complicated coalworkers pneumoconiosis, indicative of exacerbated inflammatory R.OM production (Thomas and Evans, 1975). Experimental asbestos inhalation in rats leads to an adaptive but evidendy insufficient response by an increase in endogenous antioxidant enzymes (Janssen etal., 1990). Protection of the vascular endothelium against iron-mediated ROM generation and injury is afforded by the iron sequestiant protein ferritin (Balia et al., 1992). 

O Neill P (1983) Pulse radiolytic study of the interaction of thiols and ascorbate with OH-adducts of dGMP and dG. Implications for DNA repair processes. Radiat Res 96 198-210 O Neill P (1984) Hydroxyl radical damage potential repair by sulphydryls, ascorbate and other antioxidants. Life Chem Rep Suppl Ser 2. In Rotilio G, Bannister JV (eds) Oxidative damage and related enzymes. Life Chem Rep 1 337-341... 

Two main mechanisms are generally proposed for copper induced changes to the plasma membrane function direct effects on sulphydryl groups of membrane constituents and direct or indirect free radical mediated lipid peroxidation. 

De Vos et al. (1989) suggest that the copper-induced damage to the permeability barrier in roots of Silene cucubalus is caused by a direct metal action on both membrane lipids and thiols. They propose that the first damaging effects of copper ions is the oxidation and cross-linking of membrane protein sulphydryls. However, they also adjudge an important role to the copper induced membrane lipid peroxidation, possibly due to direct free radical formation in the membrane this effect could be enhanced by a depletion of thiols such as glutathione which results in a concomitant decrease of the cellular defence system against free radicals. 

Ribonucleotide reductase catalyses the reduction of the four common ribonucleotides to their corresponding deoxyribonucleotides, an essential step in DNA synthesis. All four ribonucleotides are reduced by the same enzyme [77], The enzyme (250 000 mol. wt.) is a complex of two proteins Mi which contains substrate and redox-active sulphydryl groups and M2 which contains both a (x-oxo-bridged binuclear iron centre (Fig. 5) [77] and a tyrosine moiety sidechain which exists as a free radical stabilised by the iron centre [78], This radical, which is only 5.3 A away from iron centre 1, has access to the substrate-binding pocket and is essential for enzyme activity. Electrons for the reduction reaction are supplied from NADPH via thioredoxin, a small redox-active protein. 

Free radical scavenging. Albumin is a major source of sulphydryl groups thiols scavenge free radicals (nitrogen and oxygen species). 

In studies of peptides and proteins containing sulphydryl and disulphide groups irradiation at 77 K leads to non-S radicals, but on warming migration of spins to sulphur occurs and the stable radicals at higher temperature are thiyl radicals - . Other forms of energy transfer must also occur as the concentration of thiyl radicals eventually formed is higher than the total radical concentration at 77 K. 

The lipids that constitute the cell membrane, especially those lipids containing unsaturated double bonds, are susceptible to free radical attack, leading to the formation of lipid peroxides and aldehydes (Kako 1985). A number of short chain fragments produced from peroxidation of polyunsaturated fatty acids as 4-hydroxyperoxy nonenal and 4-hydroxy 2-alkenals react with sulphydryl groups of various enzymes modifying their activities. 

A regional difference in the rates of reduction of free radicals by sulphydryl groups may result in the site susceptible to development of N-methyl-hT-nitro-N-nitrosoguanidine-induced gastric cancer in male Wistar rats (Mikuni and Tatsuta 1998). 

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