The Stress—Strain Characteristics of Animal Fibers After Reduction and Alkylation

Abstract

Animal fibers were reduced to varying degrees with solutions of thiols and alkylated with methyl iodide or ethylene dibromide. The stress-strain curves of S-methylated Lincoln wool fibers showed the following characteristics. The stresses at the end of the Hookean region and yield region and the breaking stress approached zero at zero disulfide content and maintained a constant ratio. Likewise the slopes of the yield and post-yield region showed a constant ratio and extrapolated to zero at zero disulfide content. The decrease in stress or slope per disulfide bond broken was much greater at low disulfide contents than at high disulfide contents. The strains at the end of the yield region and at break increased with decreasing disulfide content and the effect of each disulfide broken was greatest at low disulfide contents. The relationship between strain at the end of the yield region and residual disulfide content was the same, within

Secondary structure of component 8c-1 of α-keratin. An analysis of the amino acid sequence

“…It is possible therefore that in the keratin microfibril the proline side chains of disulphide-linked 'polyproline' helices interact with hydrophobic residues-in the coiled-coil structures of the microfibrillar annulus and so stiffen the microfibril. It has previously been pointed out (Crewther, 1965) that the stiffness of wool fibres during longitudinal extension is markedly decreased if either the disulphide bonds in the fibre or non-covalent bonds between and within protein constituents ofthe fibre are destroyed. This i n 711 was interpreted in terms ofthe stabilization ofthe a-helices of the microfibrils by disulphide-rich components of the fibre through the mediation of non-covalent interactions.…”

Disulfide Cross-Linked Network Structure of Intermediate Filament and Matrix in Hair and Wool Cortices

“…A similar model was presented by Crewther [20], who proposed a hypothesis with no covalent cross-links between IF and KAP forming a network cross-linked with SS bonds between globular matrix proteins. However, at present, the detailed cross-linked structure of keratin fibers remains uncertain.…”

Physical and Chemical Consequences of Keratin Crosslinking, with Application to the Determination of Crosslink Density

“…For exa:mple, intra:molecular crosslinking generally indicates a globular protein. Although such a structure for the keratin :matrix has been postulated (Crewther, 1965), :more definite evidence for the kind of crosslinking present in the :matrix would test this notion.…”

“…If the disulfide crosslinking of keratins is progressively decreased or if additional crosslinks are introduced, regular changes appear in most mechanical properties such as Young's modulus, torsional modulus, yield points, break strength, and elongation to break (Feughelman, 1963;Feughelman and Mitchell, 1964;Crewther, 1965;Menefee and Yee, 1965a;Chapman, 1969;Friedman and Tillin, 1974). Those properties involving high strain are usually most affected by cystine levels, a relationship to be expected from consideration of models in which the ultimate extension depends on internal restraints such as crosslinking.…”

“…On this basis keratins from different sources, showing large variations in sulfur content and the amount of high sulfur protein present, would be expected to show related differences in mechanical properties. According to Crewther (1965) there is a common curve relating the strain at the transition between yield and post yield regions to disulfide content, for Lincoln wool, mohair, horsehair, mutant Merino wool, and human hair. The curve was extended to very low disulfide levels by using reduced, carboxymethylated fibers.…”