Sulfhydryl activation

The macromolecule containing sulfhydryl residues to be blocked or protected is dissolved in a buffer suitable for its individual stability requirements. The blocking process may be done on a purified protein or during the early stages of a purification process to protect sulfhydryl active centers from oxidation. PBS buffers containing 1 mM EDTA work well. 

The first natural sulfhydryl activator of FDPase to be described was cystamine, which at pH 7.5 was found to undergo a disulfide exchange reaction with 2 reactive cysteine residues in the protein (45), leading... 

Elastase activity is not a universal property of proteolytic sulfhydryl-activated enzymes. There are abundant reports in the literature describing the disappearance of elastic fibers in vivo preceding the repair of damaged tissues, but there is no evidence as to how this is brought about. The tissue cathepsins, most of which are SH-activated, have received little systematic study, but Thomas and Partridge (1960) reported that cathepsins extracted from kidney and spleen by the method of De La Haba et al. (1955) did not digest elastin either in the presence or the absence of cysteine. 

In the presence of inorganic phosphate and transacetylase (in crude ex tracts) acetyl phosphate is produced. Reversal of this reaction has been achieved. Since sulfhydryl activation of the liver enzyme has been noted,... 

Disulfides. As shown in Figure 4, the and h-chains of insulin are connected by two disulfide bridges and there is an intrachain cycHc disulfide link on the -chain (see Insulin and other antidiabetic drugs). Vasopressin [9034-50-8] and oxytocin [50-56-6] also contain disulfide links (48). Oxidation of thiols to disulfides and reduction of the latter back to thiols are quite common and important in biological systems, eg, cysteine to cystine or reduced Hpoic acid to oxidized Hpoic acid. Many enzymes depend on free SH groups for activation—deactivation reactions. The oxidation—reduction of glutathione (Glu-Cys-Gly) depends on the sulfhydryl group from cysteine. 

Several mucolytics reduce the viscosity of mucus by cleaving the disulfide bonds that maintain the gel stmcture. AJ-Acet l-L-cysteine [616-91 -1] (19), introduced in 1963, and mesna [19677-45-5] (20), developed in Europe in the early 1970s (20,21), are effective compounds in this class. Whereas most mucolytics must be adrninistered by aerosol, carbocysteine [638-23-6] (21), which contains a derivatized sulfhydryl group, has shown activity by the oral route (22,23). However, carbocysteine does not reduce mucus viscosity, as does acetylcysteine, but appears to have a direct action on mucus glycoprotein production (24). 

A thiol, usually under basic catalysis, can undergo Michael addition to an activated double bond, resulting in protection of the sulfhydryl group as a substituted 5-ethyl derivative. 

Displacement of the sulfhydryl group in primary thiols, like L cysteine and 2-diethylaminoethanethiol, requires elemental fluorine, the most active oxidant Elemental sulfur is the major by-product in those reactions [7] (equation 2)... 

Ford, S. R., Buck, L. M., and Leach, F. R. (1995). Does the sulfhydryl or the adenine moiety of CoA enhance firefly luciferase activity Biochim. Biophys. Acta 1252 180-184. 

When a cell extract prepared from A. nicotianae FI1612 cells was stored without the addition of sulfhydryl-protecting reagents, 80% of the initial activity was lost after storage at 4°C for 4 days. The enzyme activity was stabilized... 

Taken together, these results indicate that similar to other proton-translocating membrane proteins, both types of Na /H exchangers contain critical sulfhydryl groups that are involved in the transport mechanism. These sulfhydryl groups do not appear to be present at the external transport site but may be involved in switching from an inactive to an activated state. 

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