Thiol Groups in proteins

Peroxygens Hydrogen peroxide activity results from formation of free hydroxyl radicals ( OH) which oxidize thiol groups in enzymes and proteins Peracetic acid disrupts thiol groups in proteins and enzymes... 

Radicals can affect thiol groups in proteins and peptides in a number of different ways. The response might be formation or loss of disulphide bridges. More dramatic free radical exposure can lead to the formation of sulphenic, sulphinic and sulphonic acids. The loss of free thiol groups can be assessed utilizing the methods described here. 

Thiol groups in proteins also react with water soluble carbodiimides. For example, papain is modified at cysteine 25. Also, free thiol groups in buckwheat a-glucosidase are protected by reacting them with a carbodiimide. Tyrosine residues are also modified with carbodiimides, and the inactivation of yeast hexokinase is reversed by hydroxylamine. ... 

Leach (1964) has discussed in detail the merits of various methods for determining disulfide and thiol groups in proteins. 

Sulfenic acids (45) are generally quite unstable they easily dimerise and eliminate water to form thiol sulfinates (46) (Scheme 28). Several sulfenic acids have, however, been isolated and many of these are stabilised by hydrogen bonding to a carbonyl or amino group. The first sulfenic acid to be isolated was the anthraquinone derivative (47) in 1912. Sulfenic acids have been postulated as transient intermediates in many chemical and biochemical processes, e.g. the oxidation of thiol groups in proteins and the thermolysis of sulfoxides, including the acid-catalysed rearrangement of penicillin sulfoxides (48) to cephalosporins (49) (Scheme 29)... 

Organic acids (lactic, acetic) Bacteriocins co2 Hydrogen peroxide Diacetyl Reuterin Ethanol Increase acidity, antimicrobial compounds Nisin only bacteriocin permitted as food preservative, disrupts cytoplasmic membrane Reduces membrane permeability Oxidizes proteins Interacts with arginine-binding proteins Not confirmed, may interact with thiol group in proteins that may lead to oxidative stress (Whitehead et al., 2008)... 

In Chapter 9, we saw that vitamin C is used in diverse ways, united only by the same molecular action. This also applies to SOD, catalase or haem oxygenase. At the molecular level, their actions are always identical. The effects, however, are diverse and may serve quite different purposes. Take SOD. Its action is simple to remove superoxide radicals. But is this purely and simply an antioxidant action, or is it also a signal If the formation of superoxide radicals outstrips their removal by SOD, some of the extra free radicals will oxidize the thiol groups in proteins, sending tran-scription factors scurrying to the nucleus. In the nucleus, these transcrip-tion factors bind to DNA and stimulate the production of new proteins, which help restore the cell to health. In other words, the cell adapts to a small change in circumstances, such as a slight increase in oxidative... 

Some proteins interconvert between disulfides and thiols. Glutathione provides a major protective mechanism against oxidative stress. For example, it helps keep cysteine thiol groups in proteins in the reduced state (see here). If two thiol groups become oxidized, they can be reduced nonenzymatically by glutathione. 

The mixed disulfide hypothes for the repair action of amlnothiol drugs continued to draw support. A variety of aminothiols exchanged readily with h,U -dlthiobls(benzenesulfonlc acid) but no single correlation was found between the equilibrium reached and the antiradiation potency of the peurticular aminothiol. 9 While the presence of thiol groups in protein may be a sufficient feature for the operation of the mixed disulfide mechanism it is not a necessary feature, because amino-... 

Fluorescent reagent used for labelling thiol groups in proteins. Red prisms (EtOAc). Mp 207-208.5°. 

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