A number of the important physical and chemical properties of wool are closely associated with the presence of disulfi de cross-linkages between the polypeptide chains of the protein. This conclusion results from a study of the behavior of wool before and after alteration of the mode of linkage of the sulfur by a series of highly specific reactions.The cystine in wool can be readily reduced to cysteine with thioglycolic acid. Strongly alkaline solutions of the reagent have been shown by previous investigators t o dissolve the protein and destroy its fibro us structure. It is now shown that wool can be reduced with thioglycolic acid over a wide range of pH, and that when the reduction is carried out in neutral or acid solution, the fib rous structure of the wool is not destroyed when the disulfide groups are reduced to sulfhydryl groups. T he sulfhydryl groups of fibers reduced in this way react readily with alkyl halides to form thioether groups.Thus reaction of reduced wool with alkyl monohalides, such as methyl iodide, results in permanent rupture of disulfide linkages, and the fibers are greatly increased in extensibility and decreased in strength. Alkylation with aliphatic dihalides, such as methylene iodide or trilnethylene dibromide, introduces hydrocarbon chains between pairs of sulfur atoms of cystine molecules in the fibers. Such fibers are very similar to untreated fibers in physical properties.Wool in which the disulfide linkages have been broken by reduction, or by reduction and alkylation with alkyl monohalides, possesses much higher alkalisolubility t han untreated wool, while wool in which the disulfide cross-linkages have been replaced by new covalent cross-linkages through reduction followed by alkylation with dihalides possesses m uch lower alkali-solubility. Since th!' susceptibility of wool to degradation by alkalies is one of its greatest disadvantages, p rocesses that would make it stable toward alkalies should also enhance its durability. CONTENTS

Wool that has neither been injured mechanically nor modified chemically is completely resistant t o attack by the proteolytic enzymes-pepsin, trypsin, chymotrypsin , and papain. When the cuticle or scale layer of the fib ers is damaged by mecha nical means, the wool becomes susceptible to attack by p epsin and chymotryp sin. Under these conditions only a small portion of the wool is digested, yet the fi bers are considerably weakened and their fibrous structure is partly destroyed.Wool in which the disulfide cross-linkages have been broken, as by r eduction, or by reduction followed by methylation, is almost completely digested by p epsin and chymotrypsin, but is attacked only slightly by trypsin . When the reduced wool is reoxidized and its sulfhydryl groups are converted t o disulfide groups, the wool regains its original sta bility. When the sulfhydryl groups of the reduced wool are converted to bis-thioether groups by the action of an aliphatic dihalide, the stability of the wool toward enzymes is greatly enhanced.

Wool protein, like other fibrous proteins, is composed of long, flexible molecular chains.This flexibility appears to be the basis of the long-range elasticity of wool fibers. The wool fiber is distinguished from other textile fibers by the presence of covalent disulfide cross links between these main chains. Rupture of these links by chemical means decreases the strength of the fiber without necessarily affecting the• elastic recovery.Rebuilding the covalent linkages largely restores the original properties of the fiber.Wool appears to be analogous to rubber in several respects. Thus the stress-strain, solubility, and swelling characteristics are greatly influenced by the extent of cross linking in the two materials.

Wool protein, like other fibrous proteins. is composed of long, fle xible molecular chains. This flexibility appears to be the basis of the "long-range" elasticity of wool fibers. The wool fiber is distinguished from othu textile fibers by the presence of covalent disulfide cross-links between these main chains. Rupture of these links by chemical means decreases the strength of the fiber without necessarily affecting the elastic recovery. Rebuilding the covalent linkages largely restores the original properties of the fiber.Wool appears to be analogous to rubber in several r espects. Thus the stressstrain, solubility, and swelling characteristics are greatly influenced by the extent of cross-linking in the two materials.

Wool is remarkable among textile materials in that it possesses high extensibility and the ability to return to its original length or shape after being stretched or distorted. These properties are of advantage in such products as clothing, blankets, and carpets. It is shown that a number of the important physical properties as well as some of the chemical properties of wool are dependent upon a unique molecular structure, provided by the presence of disulfide or cystine cross-linkages between the main molecular chains of the fiber. As a result, wool fibers possess a three-dimensional molecular net-work while most other textile fibers are composed of bundles of chain-like molecules, arranged more or less parallel to the axes of the fibers. The rôle of these disulfide cross-linkages is made clear by a study of the behavior of wool before and after alteration of the mode of linkage of the sulfur. For example, the disulfide cross- linkages are readily broken to form sulfhydryl groups by the re ducing agent, thioglycolic acid. The sulfhydryl groups of the reduced fibers readily react with alkyl halides to form thioether groups with two possible results. Thus, the reaction of reduced wool with alkyl monohalides results in permanent rupture of di sulfide linkages and greatly increases the extensibility and decreases the strength of the fibers. The reaction with aliphatic dihalides introduces hydrocarbon chains between pairs of sulfur atoms of cystine molecules in the fibers. Such fibers are very similar to untreated fibers in physical properties. Wools in which the disulfide linkages have been broken by reduction, or by reduction followed by treatment with alkyl mono halides possesses much higher alkali-solubilities than untreated wool, while wools in which the disulfide cross-linkages have been replaced by new cross-linkages through reduction followed by re action with dihalides possess much lower alkali-solubilities. Since the susceptibility of wool to degradation by alkalies is one of its greatest disadvantages, practical processes that would make it stable at its cross-linkages should also enhance its durability.