Keratoses from wool

This method involves oxidation of hair using peracetic acid. Analysis of the gamma-keratose from human hair indicates a higher proportion of sulfur compared to the other keratose fractions or to whole fiber [42]. Cor-held et al. [93] have isolated matrix material from merino wool by this procedure. Chemical analysis shows a relatively high proportion of sulfur and a correspondingly greater proportion of cystine compared to the other fractions or to whole fiber [42]. 

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and threonine, occurs during extraction and accounts for some of the complexity of wool protein fractions (Lindley, unpublished observations, 1962).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 Lindley (unpublished, 1961) has shown that S -carboxymethyl cysteine isolated from acid hydrolyzates of SCM kerateines is partially racemized as measured both by direct optical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. 

Another method, the method of Alexander and Earland [115], consists of oxidation of the disulfide bonds of the keratin to sulfonic acid groups, using aqueous peracetic acid solution, and separation of the oxidized proteins, generally by means of differences in solubilities of the different components of the mixture. The first three fractions in this separation are called keratoses. The amino acid composition of these three fractions isolated from merino wool has been reported by Corfield et al. [116]. 

The extracts (SCMKB, 7-keratose) obtained by both procedures demonstrate marked heterogeneity [222,223]. SCMKB from Merino wool has been shown to contain more than 60 polypeptides [222]. These high-sulfur polypeptides have been found to display heterogeneity with respect to both molecular weight and charge. 

Many approaches are employed to extract KRs from hair or wool fibers. These methods are based on oxidative and reductive chemistries and have been published since the early 1900s. Keratoses and kerateines represent oxidized and reduced keratin derivatives, respectively, and they have been used to prepare materials for medical applications, such as wound healing, bone regeneration, hemostasis, and peripheral nerve repair (Hill et al., 2010]. The use of either oxidative or reductive extraction techniques can lead to different mechanical properties due to the absence or presence of disulfide bonds in the material, respectively. 

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