Browning disulfide bonds

Like as2-casein, /e-casein has two disulfide bonds which can form cross-links with /3-lactoglobulin. The N-terminal two-thirds of the molecule is hydrophobic and contains the two disulfide bonds. The C-termi-nal end is hydrophilic, polar, and charged. It varies in the number of attached carbohydrate moieties and has only one phosphate group. These characteristics make /c-casein ideal for the surface of casein micelles, where it is most often found. It is not susceptible to calcium ion binding, as the other caseins are, and when present on the surface of micelles, it protects the other caseins from calcium (McMahon and Brown 1984A Swaisgood 1982). 

The magnitude of the changes in longitudinal and torsional stiffness of wool caused by rupturing disulfide bonds is very dependent on the relative humidity used for stressing the fibers. In dry fibers the effects of disulfide rupture are small or not apparent (Harris and Brown, 1946 Feughelman, 1963 Feughelman and Mitchell, 1964). 

Higher concentrations of mercaptan, higher pH [43], and higher solution-to-hair ratios all produce more extensive reduction [42,44] and ultimately more tensile damage. The decrease in dry tensile properties is less than in the wet state. This is in agreement with the work of Harris and Brown [37], who showed that up to 60% elimination of disulfide bonds in keratin fibers, by reduction and methylation, produces only small effects on the dry tensile properties (65% RH). However, the wet tensile properties decrease almost linearly with the disulfide content. 

Amino acid sequence studies of BSA (Brown, 1975) and HSA (Behrens et aL, 1975 Meloun et aL, 1975) revealed the albumin molecule to consist of three compact domains held by 17 disulfide bonds arranged in... 

Fig. 8.4 Dependence of the computed average distance between the C -atoms as a function of Fq for the polypeptide model black circles), cystine (red circles), and DEDS (green circles) and obtained from force field equilibrium (at zero force) and force clamp MD (for Fq > OnN) simulations. Computational reference data for DEDS obtained from QM/MM simulations are shown by GEOMETRY FILE/created by CPMD brown triangles and the experimental reference based on the strained macrocycle [43] is marked by a violet square. The horizontal blue, pink and orange dotted lines are the average C -C distances of disulfide bonds in TDi, DO and interchain Ig proteins, respectively, whereas the cyan dotted line corresponds to intrachain Ig proteins. Reprinted from Ref. [42]...

Transannular cation radicals with the intramolecular sulfur-sulfur bond of the 2ct-1ct type generated from medium-ring disulfides like 1,5-dithiacyclooctane are an exception in terms of their stability, although they are not resistant to water (Musker 1980). ESR and resonance Raman spectroscopy studies revealed the existence of the 1,5-dithia-cyclooctane cation radical, with substantial bonding between the sulfur atoms (T. Brown et al. 1981 Tamaoki et al. 1989). Computations confirmed this statement and pointed out that the chair-boat conformer has the lowest energy as compared to other possible conformers (Stowasser et al. 1999). 

Several hundred reagents are described as being useful for substance visualization [6,27,52,53]. A relatively common test is to place the sorbent into a tank of iodine crystals. The iodine vapors form weak-charge transfer complexes with unsaturated bonds of the sample. This is visibly detected as brown spots. Reaction with iodine is generally reversible but has been shown to oxidize compounds such as mercaptans and disulfides. 

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