Cystine cross-links

Hair straightening compositions based on mixtures of ammonium bisulfite [10192-30-0] and urea [57-13-6] have been introduced and have found some apphcation in the Caucasian hair market. The reformulation of the cystine cross-links in bisulfite-reduced hair is best accompHshed by a rinse, pH 8—10, rather than by the use of oxidizing agents (66). 

Figure 20. Top left Condensed schematic diagram of human lactoferrin (hLf), with the C-lobe shown on the right and the N-lobe on the left. The a-carbons of cysteine and selected noncysteine residues are symbolized by filled and open circles, respectively. Cystine cross-links are shown as dashed lines. Unlabeled vertices symbolize carbon atoms, and hydrogen atoms are suppressed for clarity. Top right The trefoil knot derived from the C-lobe of hLf. Bottom Stereoview (Ca trace plus cross-links) of the knot shown on the top right.93 Reprinted with permission from C. Liang and K. Mislow, J. Am. Chem. Soc. 1995,117,4201. Copyright, 1995 American Chemical Society.

Chicken feathers can be converted to fibers for use in diapers.140 Each chicken produces 0.5 1.0 lb of feathers. Feathers, hides, hoofs, and hair all contain proteins containing cystine cross-links. Cured rubber containing disul-... 

Val-Cys-Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys-Asn-COO-. When only the composition is known (i.e., the sequence is unknown), the amino acids are separated by commas and enclosed in parentheses, for example, (Ala,Cys2,Gly) means a peptide containing one Ala, two Cys, and one Gly in an unknown order. A "polypeptide chain" is, by convention, a continuous chain linked only by peptide bonds. A protein may have only one polypeptide chain and then the polypeptide and the protein are synonymous. In other cases, a protein may have more than one polypeptide chain, as does insulin. In such cases, the different peptide chains within a protein may be held together by noncovalent forces, as in the case of hemoglobin, sometimes supplemented by covalent cystine cross links, as in the case of insulin. In many cases, the noncovalent interactions allow more than one conformation and a protein may switch from one conformation to another as part of its function. 

The tertiary structure is stabilized mainly by a combination of cystine cross-links (where present) and hydrophobic forces. Hydrophobic forces are generated by interactions between different regions of the polypeptide chain. For example, two a-helices may interact to form an a-helical coiled coil or a b-barrel may provide a core surrounded by a-helices, and so on. 

Cystine cross-links can be removed by reducing agents or replaced by oxidizing agents. 

The end domains contain many cysteine residues, and these form cystine cross-links with cysteine residues of KAP of the matrix. 

Figure 4—3. Rate of cleavage of cystine cross-links estimated from tensile properties [21]. Reprinted with permission of the Journal of the Society of Cosmetic Chemists.

The chemistry of bleaching shows that a major side reaction in the beaching of hair involves the oxidation of cystine cross-links to cysteic acid residues. This disruption of cross-links has a major influence on the wet tensile properties of hair. 

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