Wool, protein

Na03SS)n — [wool] — SNa + [wool]—SS03Na Wool protein Bunte salts... 

WOOL, The natural, highly crimped fiber from sheep, wool is one of the oldest fibers from the standpoint of use in textiles. Minute scales on the surface of the fibers allow them to interlock and are responsible for the ability of the fiber to felt, a phenomenon responsible for felt cloth and mill-finished worsteds. Crimpiness in wool is due to the open formation of the scales. Fine merino wool has 24 crimps per inch ( " 10 per centimeter). Luster of the fiber depends upon the size and smoothness of the scales. The basic wool protein, keratin, comprises molecular chains that are linked with sulfur. When sulfur is fed to sheep in areas deficient of the element, the quality of the wool improves. Wool fibers that fall below 3 inches (7.5 centimeters) in length are known as clothing wool fibers 3-7 inches (7.5-17.8 centimeters) long are referred to as combing wools. The wool-liber diameter ranges from 0.0025 to 0.005 inch (0.06-0.13 millimeter). See also Fibers. 

Swan153 demonstrated that sulfite or bisulfite ion reacts with sulfhydryl (SH) groups of cystine in wool protein, reducing the disulfide linkage and giving a protein fraction (P ) having one cysteine SH and a second protein (P ) on which a S-sulfo derivative of the cysteine moiety has been formed ... 

Industrial Uses. Papain is used in the leather industry to prepare the sides for tanning. Its proteolytic action removes some of the undesirable proteins which adhere to the hide and thus facilitates the subsequent tanning process. In the textile industry, the treatment of wool fibers with papain has been found to reduce the shrinkage from laundering. This appears to be caused by the abihty of the enzyme to destroy the elastic properties of wool protein. Because of its digestive action on protein, papain is used as a spot remover in the laundry and dry cleaning business. 

Owing to the economic importance of wool most investigators have used this material as a convenient source of a-keratin. When parallel studies have been made on hairs from other animals and on nails, claws, hoofs, and quills it has been found that conclusions reached by studying wool proteins apply, with only minor qualifications, to other keratinized tissues. Feathers are only of slight economic value and correspondingly less attention has been devoted to their chemistry, despite the fact that feather proteins are more readily solubilized and purified and that feather rachis yields X-ray diffraction patterns of excellent quality. 

Fig. 1. Fractionation of wool proteins at 50°C to give low-suifur fraction SCMKA2 (Gillespie and Lennox, 1953, 1955a Gillespie, 1957). All moving boundary electrophoresis runs were carried out at an ionic strength of 0.1 except in the presence of thioglycolate where the ionic strength was 0.2. The electrophoresis diagrams refer to runs in glycine-NaOH buffer at pH 11.0 except where otherwise stated.

Fig. 2. Starch-Kel eleetTophorcsis patterns of wool protein drerivativos in pH 8.6 buffer containing 8M urea. A, SCMKA B, SCMKA2 C, SCMKB (Thompson and O Donnell, 1964).

Fw. 3. Fractionation of wool proteins at 0°C to give high-sulfur fraction SCMKBl (Gillespie, 1962c). The electrophoresis diagrams refer to runs in acetic acid-sodium acetate buffer at pH 4.5. 

Preparation of High-S Wool Protein, SCMKB2- Low Temperature Method... 

Reduction in Neutral Solution. Several methods have been described for extracting protein from keratins following reduction in neutral solution. Urea-thioglycolate was used for this purpose by Jones and Mecham (1943-1944) when comparing the proteins from a variety of keratins. Thompson and O Donnell (1962b) reduced wool proteins in neutral solution and then... 

In aqueous solution phosphines reduce the disulfide bonds of wool. Almost complete reduction can be obtained in a single treatment at pH values above 4 using solutions of tris(hydroxymethyl)phosphine or tris-(diethylaminomethyl)phosphine (De Deurwaerder et al., 1964). Following reduction with substituted phosphines SCM groups can be conveniently introduced into wool by shaking with 0.1 M iodoacetate at pH 8. Extensive reduction and extraction of wool proteins can also bo obtained using phosphines dissolved in formamide. 

When the patterns of the high-sulfur wool proteins from different breeds of sheep were compared (Fig. 6) the major components were found to differ considerably in mobility, although the patterns were similar otherwise. 

Wool oxidized with peracetic acid contains 14 % less histidine, 6 % less phenylalanine, and 1 % less tyrosine than the original wool (Corfield et al., 1958), and large amounts of dialyzable nitrogen have been detected in y-keratose (Alexander and Smith, 1956). Thompson and O Donnell (1959a) found that peracetic acid not only ruptures peptide bonds in the wool proteins, but also fails to oxidize all the disulfide bonds. Performic acid suffers neither of these disadvantages and is therefore preferable. 

D. Some Properties of Wool Protein Fractions 1. Molecular Weight... 

The presence of many different C- and N-terminal groups in low concentration in wool protein preparations may be due to the presence of many protein components, the rupture of different peptide bonds in a small number of different protein molecular species, the adsorption of amino acids or peptides on the proteins, or a combination of these possibilities. 

It is possible that racemization of some of the amiiio aeids, such as cystine, serine, and threonine, occurs during extraction and accounts for some of the complexity of wool protein fractions (Lindley, unpublished observations, 1962). Performic acid, however, used in the preparation of the keratoses did not produce racemization in proteins (Hill and Smith, 1957). It has not proved possible to solve uneciuivocally the problem of whether or not the reduction and alkylation pi oceduros used in the preparation of SCM kerateiues cause racemization. Lindley (unpublished, 1961) has shown that S -carboxymethyl cysteine isolated from acid hydrolyzates of SCM kerateines is partially racemized as measured both by direct optical rotation procedures and also by the use of a C-S lyase enzyme which is specihe for the n-form (Schwinuner and Kjaer, 1960). Control experiments showed, however, that L-S-carboxymethyl cysteine itself is partially racemized on refluxing with 5 N acid, and when allowance was made for this it appeared that the amount of racemization attributable to the reduction and alkylation procedures was small (less than 5 %) even when the most drastic conditions (pH 12.5 and 50°C) were used to prepare the SCM kerateines. Since S-carboxymethyl cysteine in peptide combination may well racemize more readily on acid hydrolysis than does the free amino acid, even this may be an over-estimate, and it would seem unlikely therefore that racemization is a serious problem in SCM kerateines as presently prepared. 

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