GSH, an endogenous antioxidant protecting cells from oxidative damage, allows the sulphhydryl
groups (-SH) of proteins to maintain a relatively low level under physiological conditions and prevents them from reacting with free radicals , which is essential for controlling the redox state of cells .
As we predicted, only TRPA1 induced [[[Ca.sub.2+]].sub.i] responses to hyperoxic solution prepared by bubbling with [O.sub.2] gas, although [O.sub.2] differs from reactive disulphides in that it snatches an electron from a Cys sulphhydryl group rather than electrophilically attacking the group.
A possible chemical process behind this is that sulphhydryl groups of Cys633 and Cys856 are initially oxidized by hyperoxia into glutathione-sensitive sulphenic acid, with the subsequent conversion into relatively stable, glutathione-insensitive disulphide bonds.
Thus, free sulphhydryls of Cys633 and Cys856 act as nucleophiles to directly attack electrophiles such as [O.sub.2] and reactive disulphides, and this oxidative modification is maintained at Cys633.
This is undoubtedly the case when using nephrotoxic drugs, such as aminoglycosides (which have a direct nephrotoxic effect), amphotericin (causes distal tubule dysfunction, impaired urine concentration and potassium and magnesium wasting), cyclosporin A (a direct cellular toxin which impairs lysosome function in both proximal and distal tubules and evokes tubulo-interstitial changes), cisplatin (attaches to sulphhydryl
groups which are essential for proper enzyme function) .
Nickel exposure causes formation of free radicals in various tissues in both human and animals which lead to various modifications to DNA bases, enhanced lipid peroxidation, and altered calcium and sulphhydryl homeostasis.
The mechanisms of heavy metals toxicity through electron transfer most often involve the cross-linking of the sulphhydryl groups of proteins.
Chapters cover flotation fundamentals; the mechanism of flotation; sulphide mineral flotation; thiol collector chemistry; commercial sulphhydryl
collectors; properties of flotation froths; chemical properties of frothers; flotation modifiers; depression and activation of sulphides; mill test case histories; sulphide mill practice; non-metallic mineral flotation; and flotation testing.
Reactions with sulphhydryl groups also appear to play a role in As detoxification, as studies in various in vitro systems have shown that cellular toxicity of As is inversely related to intracellular glutathione (GSH) levels and is exacerbated by GSH depletion.
In the interaction with proteins, Pb binds primarily with sulphhydryl, amine, phosphate and carboxyl groups, with sulphhydryl having the highest affinity, and particularly vicinai sulphhydryls.
Inhibition of ALAD occurs through binding of Pb to vicinal sulphhydryls at the active site of ALAD, where Zn is normally bound to a single sulphhydryl (6).
After absorption, these enter the gastric parietal cells from the plasma where in the acidic milieu these are arranged non enzymatically to form active sulphenamide derivatives which then bind covalently to sulphhydryl
groups of [H.sup.+]/[K.sup.+] ATPase inhibiting these irreversibly.