Sulfhydryl Group


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Sulfhydryl Group

 

(or thiol group), an SH group of organic compounds. Sulfhydryl groups have great and varied reactivity. They oxidize easily, with the formation of disulfides and sulfenic, sulfinic, or sulfonic acids, and they readily undergo alkylation, acylation, and thiol-disulfide exchange. They form mercaptides upon reacting with the ions of heavy metals, and they form mer-captals and mercaptols upon reacting with aldehydes and ketones, respectively.

Sulfhydryl groups play an important role in biochemical processes. The sulfhydryl groups of coenzyme A, lipoic acid, and 4’-phosphopantotheine participate in enzymic reactions for the formation and transfer of acyl residues that are related to lipid and carbohydrate metabolism. The sulfhydryl groups of glutathione play an important role in the neutralization of foreign organic compounds and the reduction of peroxides; they are also of major importance in the fulfillment by glutathione of its function as a coenzyme. In proteins, residues of the amino acid cysteine have sulfhydryl groups. As components of the active centers of a number of enzymes, sulfhydryl groups participate in the catalytic effect of the enzymes and in the binding of substrates, coenzymes, and metal ions. The catalytic role of the sulfhydryl groups of enzymes consists in the formation of intermediates with substrates or their residues; in some oxidative enzymes, the process consists in the transfer of electrons and protons from substrates to acceptors.

The blocking of sulfhydryl groups by means of specific reagents results in partial or complete inhibition of the activity of many enzymes. Disulfide bonds (—S—S—), which are formed upon oxidation of sulfhydryl groups during biosynthesis of proteins, play an important role in stabilizing the structures of proteins, including enzymes, antibodies, and several hormones. Cleavage of disulfide bonds leads to disruption of the native structure of the proteins and to loss of the proteins’ biological activity.

REFERENCES

Torchinskii, Iu. M. Sul’fgidril’nye i disul’fidnye gruppy belkov. Moscow, 1971.
Jocelyn, P. C. Biochemistry of the SH Group. London-New York, 1972.
Friedman, M. The Chemistry and Biochemistry of the Sulfhydryl Group in Amino Acids, Peptides and Proteins. Oxford-New York, 1973.

IU. M. TORCHINSKII

References in periodicals archive ?
Kopec, "Carbonyl and sulfhydryl groups of chicken meat proteins after dietary modulation with selenium," Open Chemistry, vol.
Cellular damage results from HgII binding to sulfhydryl groups in tissue, the production of lipid peroxides, and the depletion of glutathione.
As antagonizes phosphate during ATP synthesis and also binds with sulfhydryl groups of numerous enzymes when in reduced form which are vital for cellular metabolism (Brouwer et al.
The idea is that the double bonds in the acrylate moieties would covalently bind to the sulfhydryl group of the cysteines and that the carboxyl groups would form an ionic interaction with the guanidinum moiety of arginine.
In cells, cadmium binds to metallothionein, a protein which contains 26 free sulfhydryl groups per molecule.
The activity of creatine kinase, urea and total antioxidant enzymes Superoxide Distmutase and glutathione peroxidase, and the marker of protein oxidation (sulfhydryl group content) are presented in Table 4.
Being the sulfur analogue of an alcohol group (-OH), this functional group is referred to as a thiol group or a sulfhydryl group. More traditionally, thiols are referred to as mercaptans.
Glutathione S-transferase (GST) is GSH-dependent antioxidant enzyme which catalyses the conjugation of reduced glutathione via the sulfhydryl group, to electrophilic centers on a wide variety of substrates (Karthikeyan et al., 2007).
Several enzymes in antioxidant defense systems may protect the imbalance between pro-oxidant and antioxidant but unfortunately, most of the enzymes contain sulfhydryl groups at their active site hence become inactive due to direct binding of lead to sulfhydryl group (58).
Similarly, persons who are homozygous for apolipoprotein E4, which has no sulfhydryl group, might have a lesser capacity for eliminating xenobiotics dependent on binding to sulfhydryl groups, such as heavy metals and some xenobiotic chemicals.
Fragments of furin containing the aforementioned cysteine residues were isolated and tagged with iodoacetamide, which attaches to the free sulfhydryl group in cysteine residues not involved in a disulfide bond.
Penicillamine and captopril, both containing a sulfhydryl group, have been implicated in ageusia.[7] Ageusia has also been associated with transdermal nitroglycerin.[8] Tetracycline and metronidazole have been associated with a metallic taste.[9,10] Dysgeusia secondary to acetazolamide therapy has previously been described only once in the English language literature.[6]