Reduction of disulphides

Bockle, B. and Muller, R. (1997). Reduction of disulphide bonds by Streptomyces pactum during growth on chicken feathers. Appl. Environ. Microbiol. 63,... 

Another example is the reduction of disulphides to thiols (e.g. disulfiram is converted to diethyldithio-carbamic acid). 

Finally, disulphide bonds can be located by hydrolysing a protein to a mixture of peptides using either a proteinase or a specific chemical method of cleavage and the mixture can be analysed directly by fast-atom bombardment mass spectrometry (Chapter 3) and again after reduction of disulphide bonds (Yazdanparast et al., 1987). By identifying those peaks which disappear as a result of reduction and new peaks with appropriate masses that have taken their place, it is simple to assign disulphide bonds to the relevant amino-acid sequences. 

For preparing whole ricin IT, the intact toxin is normally derivatized with a bifunctional cross-linking agent before being mixed with antibody prepared for cross-linking by partial reduction of disulphide bonds [183]. 

The effects of dimethyl sulphoxide, lithium bromide, guanidinium chloride, sodium dodecyl sulphate, and urea on lysozyme have been studied using Raman spectroscopy. The spectrum observed was found to depend on the denaturant used, suggesting there is not a unique denatured state for lysozyme. An analysis of the interaction of sodium dodecyl sulphate with lysozyme has been published. A kinetic study of the denaturation and subsequent reduction of disulphide bonds in lysozyme has been made using rapid ultrasonic absorption measurements. 

The reduction of disulphides on D.M.E., the reverse of equation (2), appears to be a simpler reaction and in some cases a single cathodic wave was observed which behaves as required by a reversible process however, in many other cases evidence for irreversible processes was found . Moreover, in some conditions cystine as well as other disulphides present a pre-wave. 

A much more detailed discussion of the reduction of disulphides to mercaptans is given in Chapter 4 on the preparation of thiols. 

Reduction of disulphide bonds followed by alkylation of the free cysteines to prevent reoxidation, while not essential for the digestion of most proteins, generally gives better results. This is due to increased susceptibility of the reduced/alkylated protein to tryptic digestion and the absence of any disulphide-linked peptides (which are not matched in the database search) from the PMF data (6). 

In general, the rate of reduction of disulphides by phosphines in aqueous solvents decrease in the order PR3 > PR2Ph > PRPh2 > PPhs (where R = alkyl). 

PH3 itself is cytotoxic and used as a fumigant against pests in stored products. It inhibits mitochondrial respiration but the details of the process are unclear. The oxidation pathways for PH3 differ significantly from those of tertiary phosphines PR3 and for these the available pathways depend on the substituents R. Pathways involving radicals usually lead to p-sdssion when R = aryl but a-scission when R = alkyl. The autoxidation of alkyl phosphines is usually rapid compared to aryl phosphines. Similar differences exist in the reduction of disulphide bonds the alkyl derivatives are more reactive. 

Reduction of disulphides to component thiols remains an important topic for study, and PhaP " or BusP " are suitable in aqueous media for reduction of disulphides and for preventing autoxidation of thiols on storage. Quantitative reduction of disulphides by an insolubilized thioP is an ingenious procedure likely to be much used in biochemistry. 

The ability of agents so diverse as trypsin (which causes irreversible peptide cleavage) and dithiothreitol (DTT),(which presumably leads to a reduction of disulphide bridges) to activate the ATPase allows us to differentiate between these possibilities. We show below that light triggered ATPase activity Sybesma, C. (ed,). Advances in Photosynthesis Research Vol. IL ISBN 90-247-2943-2,... 

Ziegler, D.M. (1985). Role of reversible oxidation-reduction of enzyme thiol-disulphides in metabolic regulation. Annu. Rev. Biochem. 54, 305-329. 

A development reported recently [519] involves reduction of the cystine disulphide bonds in wool with either thioglycolic acid or tetrakis(hydroxymethyl)phosphonium chloride to form thiol groups, followed by crosslinking with bifunctional reactive dyes. This gave improved insect resistance but had adverse effects on physical properties such as strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. 

Sulphur dyes in the insoluble disulphide form and the Cl Solubilised Sulphur brands are reduced by the dyer as part of the application procedure. In the case of the Cl Leuco Sulphur brands reduction has already been carried out by the manufacturer, so that they are substantially in a form suitable for immediate application (section 1.6.2) The chemistry of the reduction of sulphur dyes is complex, as is the chemistry of the dyes themselves it has been well described elsewhere [204]. It is possible to describe the state of a reduced sulphur dye in alkaline sulphide or polysulphide solution by the general formula 12.42, but there are certain complications. In many cases the chromogen is not itself reduced, but in others, notably reddish browns, blues and navy blues based on indophenols, the chromogenic... 

Reduction of the adhesion level will occur if certain compounding ingredients are not avoided. The acceleration system has a direct effect on the adhesion level dibenzothiazole disulphide (MBTS) gives the highest adhesion levels. If a second accelerator is used, e g., tetramethyl thiuram disulphide (TMTD) or diphenyl guanidine (DPG), then the adhesion is significantly affected. Other ingredients which cause problems are plasticisers and process oils. 

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. 

Oximes RCH=NOH are produced in the reduction of nitroalkanes RCH2NO2 by carbon disulphide in the presence of triethylamine461 or wet potassium carbonate and... 

The mixed-potential model demonstrated the importance of electrode potential in flotation systems. The mixed potential or rest potential of an electrode provides information to determine the identity of the reactions that take place at the mineral surface and the rates of these processes. One approach is to compare the measured rest potential with equilibrium potential for various processes derived from thermodynamic data. Allison et al. (1971,1972) considered that a necessary condition for the electrochemical formation of dithiolate at the mineral surface is that the measmed mixed potential arising from the reduction of oxygen and the oxidation of this collector at the surface must be anodic to the equilibrium potential for the thio ion/dithiolate couple. They correlated the rest potential of a range of sulphide minerals in different thio-collector solutions with the products extracted from the surface as shown in Table 1.2 and 1.3. It can be seen from these Tables that only those minerals exhibiting rest potential in excess of the thio ion/disulphide couple formed dithiolate as a major reaction product. Those minerals which had a rest potential below this value formed the metal collector compoimds, except covellite on which dixanthogen was formed even though the measured rest potential was below the reversible potential. Allison et al. (1972) attributed the behavior to the decomposition of cupric xanthate. 

The method described here is based on two reactions first, the reduction of the disulphide bond between Hey and other thiols or the cysteine residue of proteins by the reducing compound tri-n-butylphosphine (Fig. 2.2.2a) followed by the reaction of Hey and other thiols with the flourogenic thiol-specific reagent ammonium... 

Mercaptoquinoline (2H2O, thioxine) [491-33-8] M 197.3, m 58-59°. Easily oxidised in air to give diquinolyl-8,8 -disulphide (which is stable). It is more convenient to make 8-mercaptoquinoline by reduction of the material. [Nakamura and Sekido Talanta 17 515 1970]. 

When sulphur dioxide alone is passed over carbon at a red heat the latter undergoes partial oxidation, the products being carbon monoxide, carbon oxysulphide and carbon disulphide no oxysulphide is obtained at a white heat.2 Both carbon monoxide and methane are oxidised by sulphur dioxide at high temperatures with formation of sulphur. It has been suggested that volcanic sulphur may, in part, be formed by the reduction of sulphur dioxide by methane, carbon monoxide and hydrogen, all of which are emitted by volcanoes.4... 

Thioformaldehyde, (H2CS)3, results from the reduction of carbon disulphide by nascent hydrogen.4... 

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