Sulphydryl reagents

Gailis, M. and Nguyen, M.-H. (1975). The effect of sulphydryl reagents on the heart rate and coronary flow of the isolated perfused guinea pig heart. Arch. Int. Pharmacodyn. Ther. 218, 19-28. 

Mercuric chloride is thought to gain access to the intracellular compartment through Na + and Ca2 + channels in the membrane [ 100]. Sulphydryl reagents, including Hg2 +, could inhibit K +-stimulated uptake of Ca2+ into rat brain synaptosomes in vitro [101]. In muscle sarcoplasmic reticulum, Hg2+ causes inhibition of ATP-dependent Ca2 + uptake and loss of accumulated calcium [ 102,103]. However, HgCl2 has been found to inhibit ATP-dependent calcium uptake more strongly than it inhibits potassium-stimulated uptake [ 104],... 

Martin (1971) found that the transport of choline across the red cell membrane was inhibited by N-ethylmaleimide (NEM), a sulphydryl reagent which covalently modifies cysteine residues in proteins. The extent of the inhibition depended on... 

The pharmacological tools to detoxify arsenicals are sulphydryl reagents. The classic drug for that purpose is 2,3-dimercapto-l-propanol, dimercaprol (British antilewisite, BAL). Since this compound has side effects and a low safety ratio, new analogs with less adverse effects have been developed, e.g. dimercaptopropanesulphonate, dimercaptosuc-cinic acid and dithioerythritol . The efficiency and toxicity of these agents need to be further evaluated. 

Other drugs affect intracellular calcium channels of the endoplasmic or sarcoplasmic reticulum, e.g. inositol triphosphate receptor channels open in response to InsPs itself and certain other inositol phosphates, are sensitized by thiomersal (which increases the sensitivity of the receptor to InsPs by acting as a sulphydryl reagent) and antagonized by heparin. The various ryanodine receptor channels, at which a putative natural agonist is cyclic adenosine diphosphate ribose (cADP-R), are activated by caffeine and low concentrations of ryanodine (but antagonized by high concentrations of ryanodine and ruthenium red). 

Figure 4.29 Models of IgG, IgA, IgD, IgE and IgM. (a) Structural model of IgGj before and after fragmentation by pepsin and papain and reduction with a sulphydryl reagent. Solid black chain portion = variable regions light chain portion = constant regions. Small black lines represent disulphide and half-cystine (—SH) groups. Small black dots in Fc regions represent attached carbohydrate groups. The various parts of the model are labelled, (b) The structure of four classes of immunoglobulins are shown with monomeric IgA, dimeric IgA and secretory IgA. Location of the J-chain, secretory component (SC) and carbohydrate is approximate.

A Bacillus species synthesizes two activities that degrade the cell walls of Rhizopus species one of them, a chitosanase, is active towards glycolchitosan and chitosan. The activity of the enzyme (mol. wt. 3.1 x 10, p7 8,30, pH optimum 5.6, temperature optimum 40 °C) was destroyed by sulphydryl reagents, but it was restored by either reduced glutathione or cysteine. The enzyme appears to act by an f>/ (7o-mechanism. 

Normal values for serum creatine kinase published from various laboratories have differed widely owing to the multiplicity of procedures available for its determination. The chemical reaction catalysed by the enzyme is freely reversible and can be readily measured in either direction. The reaction of creatine phosphate with ADP (to form creatine and ATP) is several times faster than the reverse reaction and is therefore to be preferred on grounds of sensitivity. The addition of a sulphydryl reagent such as cysteine to the reaction mixture [122] to protect the enzyme has often been omitted, which usually leads to lower values. The inclusion of cysteine is particularly important in the case of serum samples which are not perfectly fresh, since it serves to restore the enzyme to its original activity. Under these conditions samples that have been posted the previous day or stored frozen for two or three weeks are satisfactory. Slight haemolysis of samples is unimportant since red cells contain little of the enzyme. 

Moroney JV, Carlos S, Andreo Vallejos H and McCarty RE (I98O) Uncoupling and Energy Transfer Inhibition of Photophosphorylation by Sulphydryl Reagents, J. Biol. 255, 6670-667. ... 

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