Chemical Reactions of Keratin Fibers

Degradation of wool byHofmannophila pseudospretella (lepidoptera: Oecophoridae) larval midgut extracts under conditions simulating the midgut environment

“…That regeneration of active enzyme is most rapid with sulfhydryl reagents and at increasingly negative ORP (or higher pH), i.e., at higher concentrations of the active form of the reducing agent (presumeably RS-), supports this hypothesis. This mechanism would explain why sodium dithionite, which generates a very negative ORP, does not support rapid solubilization since it should reduce the enzyme cystine disulfide to cysteine plus a substituted cysteine thiol (Asquith and Leon, 1977;Maclaren and Milligan, 1981). Thiosulfate, sulfide, and sulfite anions react with disulfides to yield similar products and the enzymatic activity/ regeneration of disulfide could be reduced/slowed by these substituted thi01s.…”

Influences of the Glassy and Rubbery States on the Thermal, Mechanical, and Structural Properties of Doughs and Baked Products

“…Preferential plasticization of the predominantly amorphous matrix upon hydration results in dramatic reduction of the modulus and enhancement of the extensibility of keratinous tissues at moisture contents above 10%. The effect of keratin architecture on the most important chemical reactions of keratin fibers, thiol-disulfide exchange reactions, is also attributed to their two-phase structure (Asquith and Leon, 1977). The equilibrium constant for exchange reactions of accessible thiols and disulfides of proteins in dilute solution is near unity, so kinetics and cooperativity of steric factors govern thioldisulfide exchange and thiol-disulfide chain reactions in the concentrated environment of the keratin architecture (Friedman, 1973;Ziegler, 1977;Whewell, 1977).…”

The Reactivity of Human Hair. A Review

“…On the other hand, carboxymethylation of reduced hair, due to diffusion considerations, is much slower, thus setting the stage for competitive alkylation with other amino-acid residues (Maclaren et al 1968). Under similar conditions, S-cyanoethylation (reaction with acrylonitrile) is fast, specific, and more selective than iodoacetate (Asquith and Leon 1977). This selectivity was exploited in "swelling titration" of reduced hair (Wolfram and Underwood 1966) as well as in the analytical procedure devised for sulfite-treated hair (Sokol et al 1974).…”

“…The experimental evidence also suggests that the f3-elimination mechanism accounts best for the observed results. Consequently, it has been acknowledged (Swan 1957a, Asquith and Leon 1977, Nashef 1977 as the main, if not only, mechanism for the alkali-mediated changes in combined cystine of proteins. The reaction sequence illustrating f3-elimination is as follows: The dehydroalanine residues that are formed in the process of alkaline decomposition of cystine are capable of reacting not only with other side chains present in keratin to form new cross-links (lanthionine, lysinoalanine), but also with other species present in the reaction medium (Asquith and Carthew 1972).…”