Amino Acids in wool

Amino acid SCMKA SCMKB Free amino acids in wool roots Inner root sheath protein... 

Blackburn and Lee (1954) using hydrazinolysis showed qualitatively that alanine, glycine, serine, and threonine were present as C-terminal amino acids in wool, and Kerr and Godin (1959) obtained similar results from human hair and horsehair. A more thorough study by Bradbury... 

Different content of amino acids in wool fibers promotes the feamres of their chemical properties. Of the great importance is the quantity of cystine containing virtually all sulfur, which is extremely important for the wool fiber properties The higher sulfur content in the wool is, the better its processing properties are, the higher resistance to chemical and other impacts is and the higher plysic-mechanical properties are ... 

Wool has a complex chemical stmcture, composed mainly of a large number of different proteins (87). It is amphoteric in character because of the presence of basic amino and acidic carboxyl groups in the side chains of some of the component amino acids. In an aqueous acidic dyebath, protonation of the amino and carboxyl groups results in a net positive charge on the fiber. 

The great leap forward for chromatography was the seminal work of Martin and Synge (7) who in 1941 replaced countercurrent liquid-liquid extraction by partition chromatography for the analysis of amino acids from wool. Martin also realized that the mobile phase could be a gas rather than a liquid, and with James first developed (8) gas chromatography (GC) in 1951, following the gas-phase adsorption-chromatographic separations of Phillips (9). 

Zahn et al. [58, 59] have reported that thioglycolate can accelerate the rate of formation of thioether residues (lanthionyl) in wool fiber. Therefore, one might expect to find trace quantities of this amino acid in hair permanent-waved in an alkaline medium. Chao et al. [60] have demonstrated small quantities of lanthionine and carboxymethyl thiocysteine in hair reduced by thioglycolic acid. 

Table 2-8. Amino acids in intercellular cement of hair and wool fiber [79, 80].

The C-terminal amino acids in human hair have been identified by Kerr and Godin [90] using the hydrazinolysis method of Niu and Fraenkel-Conrat [93]. These amino acids are threonine, glycine, alanine, serine, glutamic acid, and aspartic acid. Interestingly, all six of these amino acids also serve as N-terminal residues. These same six C-terminal amino acids have been identified as C-terminal residues in wool fiber [94]. 

Keratins are classified into two types. The a-keratins are the main proteins of wool and hair. The P-keratins occur in feathers, skin, beaks and scales of most birds and reptiles. These proteins are very rich in the sulphur-containing amino acid cysteine wool protein, for example, contains about 4 per cent of sulphur (see p. 373). 

The amino acids in hydrolysates of wool and similar fibres can be determined by the method given in Chapter VI, and the proteins in degradation products or in water extracts by the Brdi ka reaction. 

Human hair, powdered human callus, and wool fibers were degreased by solvent extraction before incubation with the surfactants in order to make proteins easily accessible for binding. The amount of surfactant bound to the keratinic substrate was determined, as well as the denaturing effect of the surface agent on the protein with release of amino acid in the solution. Details about the procedure are given by Dominguez et al. [2],... 

The amino acid composition of wool fibres is given in Table 4.10. For different animal fibres, the cystine content of the keratin varies, but it is higher than in any other protein. There are differences in the structural positions of the amino acids in the keratin between the hair from different animal species, and also along the fibres. 

Exposure to microorganisms during 28 days leads to wool fiber degradation and, consequently, to noticeable mass reduction of all amino acids in the fiber composition. To the greatest extent, these changes are observed for coarse wool, where total qrrantity of amino acids is reduced by 10-12 rel. %, and for merino wool slightly lower reduction (4.7 rel. %) is observed. 

It should be noted that at comparatively low reduction of the average amormt of amino acids in the system (not more than 12 rel. %) all types of wool fibers demonstrate a significant reduction of the qrrantity of some amino acids, such as serine, cystine, methionine, and son on. (up to 25-33 rel. %). 

Kantouch, a. a., and A. Bendak Action of Periodic Acid and its Salts on Wool. II. Amino Acids in Periodate-oxidized Wool. Text. Res. J. 39, 851-858 (1969). 

Protein Components. The simplest picture of the proteinaceous components is one of polypeptides, which are composed of a-amino acid residues. It is estimated that wool contains about 170 different types of polypeptides varying in molecular mass from below 10,000 to greater than 50,000 (34). Complete acid hydrolysis of wool yields 18 amino acids, the relative amounts of which vary considerably from one wool to another. Typical figures for two different samples of wool are given in Table 7. 

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