Disulphide linkage

These polymers are very sensitive to mastication. Mastication decreases the solution viscosity and increases the ease of solution. Because the reactive sulphur linkages, rapid vulcanizing properties are obtained. On the other hand, the presence of thiuram disulphide improves the resistance of CR to dehydrochlorination. 

Although many types of dye contain sulphur other than in sulphonic acid groups, sulphur dyes are usually considered to be those dyes that are best applied from a sodium sulphide dyebath. Like vat dyes, sulphur dyes are water-insoluble before and after application to cellulosic fibres. Disulphide linkages in the dye molecules are readily reduced by sodium... 

General.—Triethyl phosphite has been used to achieve stepwise O-ethylation of phosphoric and benzylphosphonic acids.5 The disulphide linkage in bis(phosphinyl) disulphides is cleaved by ammonia in a suitable solvent to yield the phosphinyl-sulphenamides (l).6... 

Figure 3.31. Separation of proteins by SDS-PAGE. Protein samples are incubated with SDS (as well as reducing agents, which disrupt disulphide linkages). The electric field is applied across the gel after the protein samples to be analysed are loaded into the gel wells. The rate of protein migration towards the anode is dependent upon protein size. After electrophoresis is complete, individual protein bands may be visualized by staining with a protein-binding dye (a). If one well is loaded with a mixture of proteins, each of known molecular mass, a standard curve relating distance migrated to molecular mass can be constructed (b). This allows estimation of the molecular mass of the purified protein. Reproduced by permission of John Wiley Sons Inc. from Walsh (2002)...

X-ray diffraction analysis shows the protein to be a globular structure, consisting of four a-helical stretches interrupted by bends and loops. It appears devoid of any //-conformation and contains a single stabilizing disulphide linkage involving cysteine numbers 58 and 105 (Figure 5.1). 

The biological activities of several other interleukins also render them likely candidates for therapeutic application. IL-5 represents one such candidate. IL-5 is a 115 amino acid glycoprotein produced mainly by activated T lymphocytes and also by mast cells. It functions as a homodimer, exhibiting a molecular mass of 45 kDa. The individual polypeptide chains interact non-covalently and the overall dimeric structure is stabilized by two interchain disulphide linkages between cysteines 42 and 84 of each chain. Removal or alterations of the cytokine s carbohydrate side-chain does not appear to affect its biological activity. 

NGF is the prototypic neurotrophin. The mature NGF polypeptide contains 120 amino acids, exhibits a molecular mass of 26 kDa and a pi of approximately 10. It contains three intra-chain disulphide linkages, which are essential for activity. NGF is synthesized and released from target tissues of sympathetic neurons and cholinergic basal forebrain neurons. It is also synthesized by non-neuronal tissue, including salivary glands, the prostate and mast cells. It functions to... 

Mature insulin consists of two polypeptide chains connected by two interchain disulphide linkages. The A-chain contains 21 amino acids, whereas the larger B-chain is composed of 30 residues. Insulins from various species conforms to this basic structure, while varying slightly in their amino acid sequence. Porcine insulin (5777 Da) varies from the human form (5807 Da) by a single amino acid, whereas bovine insulin (5733 Da) differs by three residues. 

The insulin receptor is a tetrameric integral membrane glycoprotein consisting of two 735 amino acid a-chains and two 620 amino acid )S-chains. These are held together by disulphide linkages (Figure 8.2). The a-chain resides entirely on the extracellular side of the plasma membrane and contains the cysteine-rich insulin-binding domain. 

A variant of this procedure is provided by the preparation of S-benzyl-l-cysteine (Expt 5.206). The required thiolate salt is prepared by the reductive cleavage with sodium in liquid ammonia of the disulphide linkage in the amino acid, (S)-cystine, and is alkylated in situ with benzyl chloride. The preparation of this S-benzyl derivative constitutes a method of protection of the thiol grouping in cysteine. 

The introduction of redox-sensitive linkages, such as the disulphide group, has been used to prepare liposomes that are susceptible to the lower intracellular redox potential relative to the extracellular environment. Symmetrical disulphides are synthesised by oxidation of thiol-containing structures [64, 130, 131] (see Fig. 7),... 

The conformational dependence of the 33S isotropic a in dimethyldisulphide, (CH3)2S2, has been studied by HF calculations using the IGLO method.121 (CH3)2S2 is a good model for the disulphide linkage in polypeptides and proteins. 33S a has been calculated as a function of the dihedral angle C-S-S-C. Predicted chemical shifts vary between —84.4 ppm (< C-S-S-C = 0°) and —42.3 ppm (Calculated values refer to CS2 and cannot be converted to the SO4 scale, since the absolute shielding of the SQj anion has not been reported... 

Figure 4 Structural features and diversity of bacteriocins. Solution NMR structures are shown for (a) the lantibiotic actagardine (PDB code 1AJ1) the pedocin-like bacteriocins (b) curvacin A (PDB code 2A2B) and (c) leucocin A (PDB code 1CW6) (d) the A and B chain of the two-chain bacteriocin lactococcin G in DPC micelles (PDB codes 2JPJ and 2JPK) and the cyclic bacteriocins (e) subtilosin (PDB code 1AJ1) and (f) AS-48 (PDB code 1E68). Disulphide bonds and lanthionine linkages are shown in ball-and-stick. Chain termini are labelled N and C and the cyclisation points on the cyclic peptides are labelled with residue numbers.

The mustard family (Brassicaceae) PIPs are 7 kDa proteins with 8 cysteines in highly conserved positions that form 4 disulphide linkages in a particular pattern of connectivity. The mustard PIPs are variously potent inhibitors of serine proteases such as trypsin, chymotrypsin, thrombin, plasmin and blood clotting factors Xa and Xlla [515, 520] (Table 15). 

The squash family (Cucurbitaceae) family of serine PIPs are very small circa 3 kDa), cysteine-rich proteins (6 cysteines being involved in 3 disulphide linkages) [537-561]. These small proteins have extraordinary affinities for the target serine proteases (K values in the nanomolar and picomolar range) (Table 17). The serine proteases variously inhibited by squash family PIPs include elastase, trypsin, kallikrein and blood clotting protease factors Xa, XIa and Xlla (Table 17). Of particular note are the squash family PIPs MCoTI-I and MCoTI-U from Momordica cochinensis... 

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