Keratin, wool

Considerable doubt exists as to whether wool can be regarded as a single protein or whether it is a mixture of different insoluble proteins, so that it is perhaps not one of the most suitable proteins to study by partial hydrolysis methods. However, because of its practical importance the Leeds workers have applied their newer methods to it, and a number of peptides have been identified. 

Acidic Peptides Identified from Wool (Consden et al., 1949) 

Consden and Gordon (1950) have studied the cysteic acid peptides derived from the cystine peptides of wool as described on p. 40. After a preliminary group separation of the cysteic acid peptides by iono-phoresis, each fraction was fractionated on paper chromatograms with phenol and collidine. In Table VII are listed the peptides considered to be probably present and their approximate yield. The results were more clear-cut in this case than with the aspartic and glutamic acid 

It is clear from the results that the structure of wool is extremely complex. Almost all of the monoamino acids occur linked to both sides of glutamic and cysteic acids. The small number of aspartic acid peptides identified is probably due to the lower content of aspartic acid in wool so that the peptide spots would probably be faint and would not show on the chromatograms. 

Cysteic Acid Peptides from Wool (Consden and Gordon, I960) 

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The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

Penetration of dimethyl phosphite into the fibre, accompanied by decomposition of salt linkages and elimination of structural water in a multi-step hydration process. New salt linkages are formed between cationic groups in wool keratin and anionic dimethyl phosphite. 

Formation of covalent bonds between dimethyl phosphite, glucose and amino groups in wool keratin, stabilising the loosened fibre structure. 

Amino acid Egg white Egg yolk Casein Animal glue (collagen) Wool (keratin) Silk (fibroin) Garlic... 

Moore, J.F., and Ward, W.H. (1956) Cross-linking of bovine plasma albumin with wool keratin. /. Am. Chem. Soc. 78, 2414. 

Wool grease, 26 208-209 alcohols from, 2 2 Wool keratin... 

Dichromate anions are readily absorbed under acidic conditions by wool that has been dyed with chrome dyes. The chromium(VI) on the fibre is then gradually reduced by the cystine residues in wool keratin to chromium(III) cations, which react with the dye ligands to form a stable complex. In this way the cystine disulphide bonds are destroyed, resulting in oxidative degradation of the wool fibres [71]. 

Figure 7.3 Nucleophilic sites in wool keratin for reaction with dyes...

Room temperature phosphorescence can be observed from dried proteins. Sheep wool keratin(47) has a phosphorescence lifetime of 1.4 s. Six lyophilized proteins were shown to exhibit phosphorescence at room temperature.(48) The spectra were diffuse, and the lifetime was non-single-exponential, which the authors interpreted as due to inhomogeneous distribution of tryptophans. As the protein was hydrated, the phosphorescence lifetime decreased. This decrease occurred over the same range of hydration where the tryptophan fluorescence becomes depolarized. Hence, these results are consistent with the idea that rigidity of the site contributes to the lifetimes. 

I. H. Leaver, On the room temperature phosphorescence of wool keratin, Photochem. Photobiol. 27, 439 143 (1978). 

Figure 1 Polarized IR Spectra for (A) a-Helical Wool Keratin and (B) p-Sheet Stranded Bombyx mori Silk Thread 18 ...

Morrison and co-workers (33) measured the heat of wetting of silk fibroin and wool keratin in water as a function of their water content. Their data received proper thermodynamic treatment except that heats of solution are presumed absent. It is likely that solution effects are absent or small if zero heats are found for the immersion of samples equilibrated near the saturation pressure of water. 

Bonding Forces Between Dye and Fiber. Dye anions can participate in ionic interactions with fibers that possess cationic groups. However, the formation of ionic bonds is not sufficient to explain dye binding, because compounds that can dissociate are cleaved in the presence of water. Secondary bonds (dispersion, polar bonds, and hydrogen bonds) are additionally formed between dye and fiber [47], Close proximity between the two is a prerequisite for bond formation. However, this is counteracted by the hydration spheres of the dye and of wool keratin. On approach, these spheres are disturbed, especially at higher temperature, and common hydration spheres are formed. The entropy of the water molecules involved is increased in this process (hydrophobic bonding). In addition, coordinate and covalent bonds can be superimposed on secondary and ionic bonds. 

Hair. Until recently, the application of luminescence specifically to the analysis of human hair has not been attempted in any systematic manner. It has been shown that three of the amino acids, i.e., phenylalanine, tyrosine, and tryptophan, found in hair protein both fluoresce and phosphoresce (15). It has been established that for other proteins that contain all three of the amino acids, the luminescence (both fluorescence and phosphorescence) is predominately the result of the tryptophan chromophores, with possibly some contribution from the tyrosine (15)- More directly related to the luminescence of hair are the-studies of Konev (23) involving the luminescence of wool keratin. He observed both fluorescence and phosphorescence from wool fibers that were characteristic of tryptophan. 

Horrocks, A.R. and Zhang, S. 2004. Char formation in polyamides (nylons 6 and 6.6) and wool keratin phosphorylated by polyol phosphoryl chlorides. Textile Res. J. 74 433 441. 

Ionic liquids have also been used to dissolve other biologically occurring polymers. Wool keratin, an unbranched polymer of amino acids, has been reported to dissolve in [C4mim][Cl] up to a concentration of 11 wt% at 130 °C. Chitin has been dissolved in C4mim Ac up to 6 wt% at 110 °C [132], Proctor and Gamble has a patent on ionic liquids for the dissolution of biopolymers including chitin, chitosan, elastin, collagen, keratin and polyhydroxyalkanoate [133],... 

Boiling water can gradually break down the wool keratin and the fibre can loose... 

The titration of proteins with weak acids is not considered in this review, since in the only detailed study of the subject (Steinhardt, Fugitt, and Harris (1943) on wool keratin) the effect of selective solvation of the fiber by undissociated weak acid was added to the effect of combination with hydrogen ion. 

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