The formation of disulphide bonds

Recently, active recombinant a-LTX has been generated using bacteria in which both thioredoxin reductase and glutathione reductase are inactivated to improve the formation of disulphide bonds in expressed proteins (Li et al. 2005). The toxin is expressed as a fusion with glutathione-S-transferase (GST), which is used for affinity purification of the recombinant toxin and can be subsequently removed by selective proteolysis. Considering the relative ease of generating recombinant proteins in bacteria, this approach will facilitate structure-function studies of a-LTX. 

Leitner,. V.M., Walker, G.F. and Bernkop-Schniirch, A. (2003b) Thiolated polymers evidence for the formation of disulphide bonds with mucus glycoproteins. Eur. 

A sustained drug release is favourable for drugs with short elimination half-life. It can be controlled by hydration and diffusion mechanisms or ionic interactions between the drug and the polymeric carrier. In the case of diffusion control the stability of the carrier system is essential, as its disintegration leads to a burst release. Therefore, the cohesiveness of the polymer network plays a crucial role in order to control the release over several hours. Due to the formation of disulphide bonds within the network thiomers offer adequate cohesive stability. Almost zero-order release kinetics could be shown for insulin embedded in thiolated polycarbophil matrices (Clausen and Bernkop-Schnurch 2001). In the case of peptide and protein drugs release can be controlled via ionic interactions. An anionic or cationic polymer has to be chosen depending... 

In contrast with a i- and jS-caseins, the presence of systein residues in as2- and K-caseins leads to the formation of disulphide bonds. The number of molecules that bond to each other in K-casein differs from that in as2-casein. That is to say that in K-casein not less than 10 molecules join each other via disulphide linkages, while in most of as2-caseins only 2 molecules are linked by disulphide bonds and form a dimer. As well, intermolecular disulfide bonds have been reported for as2- and K-caseins [6, 11]. The joint of two classes of caseins for instance as2-casein-K-casein, has also been reported [6] due mainly to the different charges of C-terminal regions in these two molecules [8]. 

The mutations prevent the formation of disulphide bonds preventing normal folding of proinsuUn in the endoplasmic reticulum (ER) leading to ER stress, 3-cell apoptosis and neonatal diabetes mellitus (INS-NDM) Inactivating mutations cause decreased transcriptional activity influencing both pancreatic development and the transcription of key genes for insulin secretion (HNFIA-MODY)... 

The formation of disulphides (143) on irradiation of S-alkyl-3-oxobutanethioates (144) in benzene or ethanol appears to involve a Type I cleavage, as shown in Scheme 6, rather than direct carbon-sulphur bond homolysis. °° In contrast, the phenacyl sulphides (145) are converted in high yield into the thiones (146) via a Type II cleavage. " Examples of the... 

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. 

Oxidative bleaching of wool is invariably carried out with hydrogen peroxide. The active species involved is likely to be the same as on cellulosic substrates but specific reactions with wool amino acid residues must be considered. The primary reaction is oxidation of cystine disulphide bonds leading to the formation of cysteic acid residues (Scheme 10.41). The rupture of disulphide crosslinks, with attendant increase in urea-bisulphite and alkali solubility values, adversely affects fibre properties. As the severity of bleaching conditions increases, the urea-bisulphite solubility remains little changed but the relationships between alkali solubility and cysteic acid (Figure 10.36) and between cystine and cysteic acid (Figure... 

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