SH groups are the sulfhydryl groups, which play an essential and ubiquitous role in biology (Jocelyn, 1972). The univalent radical group, SH, is presented in many biologically active molecules, such as coenzymes and certain proteins. It is contained in glutathione, cysteine, coenzyme A, and lipoamide (all in the reduced state), and in mercaptans (R-SH). Sulfhydryl compounds are principally the sulphur-containing amino acids, which are used as radioprotective agents.

Sulfhydryl groups play an important role in biochemical processes. The sulfhydryl groups of coenzyme A, lipoic acid, and 4’-phosphopantetheine 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 fulfilment 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. Disulphide bonds (—SS—), 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 disulphide bonds leads to disruption of the native structure of the proteins and to loss of the proteins’ biological activity.

Abnormalities. Disorders or diseases caused or related.

The lower value of SH groups, the more conservative system is (i.e., there is a tendency to the development of certain diseases).

In a large number of experimental studies, it was shown that increasing radioresistance of objects, under the influence of protectors, is accompanied by an increased content of sulfhydryl (thiol) groups. This occurs not only when using thiol protectors, but also after injection of indolylalkylamines or as the result of gaseous hypoxia. Consequently, not exogenous thiol groups are used, but increasing of their endogenous content.

It gave an opportunity to consider sulfhydryl groups as natural protectors, which number largely determines the differences in the natural radiosensitivity.

A series of works by L. Revesz (Sweden) and M. Konstantinova (Russia) showed that level of radioprotective effect of some protectors and anoxia are determined by the content of SH-groups of endogenous glutathione, both during and after irradiation.

The sulfhydryl group is one of the most reactive and ubiquitous ligands in biological systems. It is found in most proteins and also in a few low molecular-weight substances such as glutathione, CoA, lipoate, thioglycolate, and free cysteine. It is the most studied of ligands, particularly in relation to their role in enzymic activity and properties of proteins. It is also involved in many membrane functions because chemical agents with a degree of specificity for sulfhydryl can disturb many functions attributed to the cell membrane. The sulfhydryl group not only constitutes a unique marker for delineating the general role of proteins in membrane functions, but it can also serve as a marker for specific functional proteins through the use of radioactive reagents that form stable bonds with sulfhydryls.

The membrane is the primary target of sulfhydryl agents because it is the first part of the cell to be exposed to them and also because it is exposed to the highest concentrations. The interior of the cell is protected from the agents by the membrane as a diffusion barrier, however. As an agent passes into and through the membrane it reacts with accessible sulfhydryls, some of which are functionally important but the majority of which are functionally inert.

Many membrane functions are disturbed by sulfhydryl agents. It can be generalized, however, that they all possess unique specificities or are associated with unique enzyme activities. They include: increase in Na+ and K+ permeabilities; inhibition of active transport of Na+ and K+, transport of sugars and Caz+, membrane ATPase and other enzymes; and blocking of antigenic effects, nerve conduction, and binding of hormones such as insulin, vasopressin, and acetylcholine.

Many recent studies have shown disorder in plasma thiol/disulphide homeostasis in the enteropathogenesis of diabetes mellitus, cardiovascular diseases, cancer, rheumatoid arthritis, chronic kidney disease, Parkinson disease and liver diseases.

In their study, Erel et al. detected high plasma disulphide values in patients who were smoking, had diabetes, obesity and pneumonia and detected low values in patients with diseases such as bladder cancer, colon cancer, kidney cancer and multiple myeloma. Disulphide values were detected as very low in rapidly growing tumors while slightly lower than normal in slow-progressing diseases.

Calculating thiol/disulphide values is an easy, inexpensive and reliable diagnostic method for inflammation and prostate cancer. Serum NT (Native Thiol), TT (Total Thiol), DD (Dynamic Disulphide) levels in patients with prostatitis and prostate cancer were found significantly lower compared to the control group. This shows that just as inflammation, prostate cancer also increases oxidative stress on tissues.

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.

Rothstein, Aser (1971). [Current Topics in Membranes and Transport] Current Topics in Membranes and Transport Volume 1 Volume 1 || Sulfhydryl Groups in Membrane Structure and Function. 135–176. doi:10.1016/S0070-2161(08)60032-5

Modig H. Cellular mixed disulphides between thiols and proteins, and their possible implication for radiation protection. Biochem Pharmacol. 1968 Feb;17(2):177–186.

FASOLD H, GUNDLACH G, TURBA F. [Carboxymethylation of sulfhydryl groups in chymotrypsin and chymotrypsinogen after splitting of the disulfide bridges by sodium borohydride]. Biochem Z. 1961;334:255–268.

CECIL R, McPHEE JR. The sulfur chemistry of proteins. Adv Protein Chem. 1959;14:255–389

Matteucci E, Giampietro O. Thiol signalling network with an eye to diabetes. Molecules. 2010;15:8890-903.

Go YM, Jones DP. Cysteine/cystine redox signaling in cardiovascular disease. Free Radic Biol Med. 2011;50:495-509.

Rodrigues SD, Batista GB, Ingberman M, Pecoits-Filho R, Nakao LS. Plasma cysteine/cystine reduction potential correlates with plasma creatinine levels in chronic kidney disease. Blood Purif. 2012;34:231-7.

Kuo LM, Kuo CY, Lin CY, Hung MF, Shen JJ, Hwang TL. Intracellular glutathione depletion by oridonin leads to apoptosis in hepatic stellate cells. Molecules. 2014;19:3327-44.

Erel O, Neselioglu S. A novel and automated assay for thiol/disulphide homeostasis. Clin Biochem. 2014;47:326-32

Mehmet Solakhan, Hülya Çiçek, Nuri Orhan, Mustafa Yildirim. Role of native Thiol, total Thiol and dynamic Disulphide in diagnosis of patient with prostate cancer and prostatitis. Vol. 45 (3): 495-502, May - June, 2019, doi: 10.1590/S1677-5538.IBJU.2018.0469