Sulphydryl-groups

All the complexes consist of several subunits (Table 2) complex I has a flavin mononucleotide (FMN) prosthetic group and complex II a flavin adenine dinucleotide (FAD) prosthetic group. Complexes I, II, and III contain iron-sulphur (FeS) centers. These centers contain either two, three, or four Fe atoms linked to the sulphydryl groups of peptide cysteine residues and they also contain acid-labile sulphur atoms. Each center can accept or donate reversibly a single electron. 

Levitt (1962) has of course proposed a theory of frost injury based on the oxidation of sulphydryl groups and the formation of intermolecular disulphide bonds and he has subsequently extended this concept to dehydration injury (see Levitt, 1972). Although popular in the 1960s and 1970s this theory appears to have lost favour in recent years. 

The conformationally sensitive sulphydryl group modified by membrane-impermeant reagents is the only exofacial sulphydryl, and as described in section 4.2.1, has been tentatively identified as Cys429 (Fig. 3). It is the most reactive sulphydryl in the... 

Na/K Pump Structure and Regulatory Role of Sulphydryl Groups... 

Cellular proteins with reactive sulphydryl groups are... 

Oxidation of enzyme sulphydryl groups by free radicals (Armstrong and Buchanan, 1978) and by the longer lived chloroamines (Weiss et al., 1983), contributes to enzymic dysfunction and to the decrease in serum sulphydryl levels, primarily mercaptoalbumin, found in coalworkers with rheumatoid inflammatory disease (Thomas and Evans, 1975). Formation of the S-nitroso adduct of plasma mercaptalbumin is thought to provide a metastable reservoir for intravascular nitric oxide release (Stamler etal., 1992). 

The mercuric ion, Hg2 +, which is obtained after oxidation in the red blood cells and other tissues, is able to form many stable complexes with biologically important molecules or moieties such as sulphydryl groups. The affinity of mercury for sulphydryl groups is a major factor in the understanding of the biochemical properties of mercuric compounds, resulting in interference with membrane structure and function and with enzyme activity. 

After injection into mice, mercuric chloride has been found to be distributed equally between erythrocytes and plasma in blood for up to 1 day after the administration [12, 13]. There is, however, a gradual increase in red blood cell/plasma ratio. In the erythrocytes, mercury is probably bound to sulphydryl groups on the hemoglobin molecule [14], though the binding is readily reversible [15]. There is possibly also a binding to glutathione [16]. 

Although mercurials are highly specific for sulphydryl groups [67-69], they are highly unspecific in terms of proteins, almost all proteins having sulphydryl groups that are metal-reactive. Thus, mercurials can disturb almost all functions in which proteins are involved [70],... 

Enzymes are important targets for mercury [71], and sulphydryl-group-containing enzyme being more sensitive to mercuric compounds than a non sulphydryl-group-containing enzyme [72], Enzymes reported to be inhibited include phosphatases [73, 74], dehydrogenases [75,76] and hexokinases [71]. 

Mercury can influence ion, water, and nonelectrolyte transport in different cells [ 14, 77]. The cell membrane is believed to be the first point of attack by heavy metals however, intracellular enzymes and metabolic processes may also be inhibited [70, 78, 79]. The attachment of heavy metals to ligands in or on the plasma membrane may result in changes in passive permeability or selective blockage of specific transport processes. Many membrane transport systems are known to be sensitive to sulphydryl-group modification [ 14, 80, 81]. 

Mercuric chloride is a very effective irreversible inhibitor of sugar transport in the intestine [87-91] partly involving a sulphydryl group in the inhibitory process [90, 91]. 

Mercuric chloride has also been shown to inhibit the enzymatic activity of soluble protein kinase A from mice brain, apparently by binding to sulphydryl groups of the enzyme [111]. The inhibition was of a non-competitive type with respect to HI histone. 

Mercury and nickel salts form many stable complexes with biologically important molecules such as those containing sulphydryl groups Chapter 5 stresses the importance and the dangers of these being formed in the skin from topical contact. The last 10 years have been a highly fertile and productive period in the discovery of antibacterial quinolones (reviewed in Chapter 6) which inhibit target enzymes at the molecular level. 

Upon activation of complement (by either the classical or alternative pathways), C3 binds covalently to the target, and an internal thioester bond in C3 is rearranged to yield a free sulphydryl group on C3 and an ester link between C3 and a hydroxyl group on the target (Fig. 3.8). The resulting co-... 

The aminophosphohpid translocase is an ATPase Il-type enzyme that requires and is activated by phosphatidylserine and to a lesser extent by phosphatidylethanolamine and is sensitive to the sulphydryl group... 

Van der Vtiet, A., Van der Aar, E.M., and Bast, A., 1991, The Upid peroxidation product 4-hydroxy-2,3-trans-l nonenal decreases rat intestinal smooth muscle function in-vitro by alkylation of sulphydryl groups, J. Pharm. Pharmacol. 43 515-517. 

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