Covalent acid‐labile crosslinkages in wool

The extent of the first stage of supercontraction of wool fibers in 8M LiBr (20°C.) was unaltered by the incorporation of 1N HCl in the solutions, whereas the extent of total supercontraction (98.5°C.) was greatly increased by the presence of HCl in the LiBr solutions. Likewise, with reduced and methylated wool, the relationship between the extent of the first stage of supercontraction and the content of residual disulfide was not affected by the presence of HCl in the solutions. When reduced and methylated wool fibers containing few residual disulfide groups were allowed to supercontract in solutions containing 8M LiBr and varying concentrations of HCl, the fibers contracted rapidly until the extent of total supercontraction in neutral solutions was approached. The rate then changed suddenly and became directly proportional to the concentration of acid in the solutions. Extensive supercontraction was observed also in alkaline solutions of LiBr if carboxyl groups of the reduced and methylated fibers were first ethylated to decrease the solubility of the wool proteins. Cortical cells, which were prepared by digesting reduced and methylated wool with crude trypsin, resembled whole wool in their behavior. It was concluded that wool contains covalent crosslinkages which are hydrolyzed by acids and alkalies. Evidence is presented that these bonds are stabilized by disulfide crosslinkages. The possiblity that disulfide interchange takes place during supercontraction in solutions of LiBr‐HCl is discussed.