Abstract
Redox regulatory system controls normal cellular functions. Controlled changes in redox couples potential serve as components for signal transduction, similarly to the phosphorylation cascade. Cellular redox biology requires both compartimentalisation and communication of redox systems: the thermodynamic disequilibrium of the major redox switches allows rapid and sensitive responses to perturbations in redox environments. The many oxidation states of sulphur are found in numerous sulphur species with distinct functional groups (thiols, disulphides, polysulphides, sulphenic, sulphinic and sulphonic acids, etc.), which participate in a complicated network of sulphur-based redox events. Human diseases such as diabetes mellitus and its cardiovascular complications have been associated with increased production of reactive oxygen species and perturbations of thiol redox homeostasis. The review surveys literature related to some etiopathogenic aspects and therapeutic perspectives. The dual toxic-protective property of sulphydryl-donor molecules in experimental settings proposes the general problem of designing antioxidants for therapeutic use.
Highlights
Redox regulatory system controls normal cellular functions
The intake of methionine might be sufficient to meet the metabolic needs of an adult individual for exogenous sulphur, since cysteine is a metabolic product of methionine catabolism
The more oxidising redox state of the endoplasmic reticulum (ER), where Protein disulphide isomerases (PDI) are found, favours only the formation and isomerisation of disulphide bonds that occurs during the folding process and is essential for proteins to reach their native structure
Summary
In the body of the reference man sulphur (S) is present in about 140 g [1]. The two principal dietary sources of S-containing compounds in human nutrition are liquids (SO42− in drinking waters) and solid. The numerous proteins containing sulphydryl groups present as thiols (-SH), disulphides (PS-SH), or as mixed disulphides (PS-SG) can influence the redox environment of the cell [4]. Cysteine in proteins plays structural roles, but can participate in redox reactions, such as thiol-disulphide exchange, single- or two-electron transfer, hydrogen-atom transfer, and nucleophilic substitution [5]. Thioredoxins (whose active site contains typically the sequence Cys-Gly-Pro-Cys) participate in redox reactions by the reversible oxidation of an active centre disulphide bond. Dithiol glutaredoxins (typical active site Cys-Pro-Tyr-Cys) are thiol-disulphide oxidoreductases kept reduced by glutathione. The more oxidising redox state of the endoplasmic reticulum (ER), where PDI are found, favours only the formation and isomerisation of disulphide bonds that occurs during the folding process and is essential for proteins to reach their native structure. Insulin resistance induced by increased inducible NO synthase in obesity may be related to S-nitrosation of insulin signalling proteins, insulin receptor, insulin receptor substrate 1 and protein kinase B (Akt) [24]
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