Amino acid composition, wool

Amino acid composition, of merino wool, 26 377t... 

Meridional tridendate ligand, 7 578 Merino wool, 26 370-371, 373, 374, 380 amino acid composition of, 26 377t Merocyanine 540 (MC540), 9 517 Merocyanine chromophores, 20 506 Merocyanine dyes, 9 503, 504, 511—512 ... 

The amino acid composition of keratin, the protein of hair and wool, includes a greater-than-average proportion of the sulphur-containing amino acid, cystine. Since this is the least soluble of the protein amino acids it can readily be isolated after carefully neutralising an acid hydrolysate of hair (Expt 5.187). Protein hydrolysis is usually effected by boiling for about 10-20 hours with 20 per cent hydrochloric acid. The hydrolysis of hair for the isolation of cystine is, however, best achieved using a mixture of hydrochloric and formic acids. 

The composition of keratins. Amino acid composition of hair, wool, horn, and other eukeratins. Ibid., 128, 181 (1939). With cooperation of D. Bolling, F. C. Brand, and A. Schein. 

The amino acid analyses of the a-, 0-, and -y-keratoses, shown in Table IV indicate that 7-keratose contains more cysteic acid, proline, serine, and threonine and less alanine, aspartic acid, glutamic acid, leucine, lysine, phenylalanine, and tyrosine than is found in oxidized wool (Corfield et al., 1958). a-Keratose in contrast contains less cysteic acid, proline, serine, and threonine, and more of the other amino acids which are present in low concentration in 7-keratose. The amino acid composition of 8-keratose is similar to that of wool. 

Amino Acid Composition of Fractions from Wool SCMK ... 

Amino Acid Compositions of Components of Wool Fibers ... 

Wright (1953) has shown that the acid-binding capacity of horn is almost identical with that of wool, but insufficient data are available, particularly with respect to amide content, to permit this value to be related to the amino acid composition of hom (Table XIV). Harrold and Pethica (1958) have observed that normal callus absorbs a little more than 1 meq of dodecyl sodium sulfate per gram in the absence of salt at pH 6.6 and almost 3 meq per gram at a total ionic strength of 0.2. Binding continues to a maximum at a concentration above the critical micelle point of dodecyl sodium sulfate. There appears to be no relationship between the large absorption in the presence of salt and the amino acid composition of callus (Table XVI). 

If the amount of acid required for titration of the "acidic side chains of wool is calculated from the amino acid composition of the fiber (Table X), the theoretical acid-binding capacity of the fiber is from 0.63 meq per gram for Merino 70 s to 0.69 meq per gram for Lincoln. The apparent discrepancy can be attributed largely to excessive values for the amide content of wool. These errors arise from the formation of ammonia by degradation of amino acids such as serine and threonine during hydrolysis. If the values of Leach and Parkhill (1956) for amide content are accepted (Table IX), the expected titration value becomes approximately 0.8 meq per gram. 

The amino acid composition of pigmented wool melanins was determined, and the effect of cationic surfactants on the reduction of bleeding of wool in alkaline solution was explained on the basis of neutralization of the carboxyl groups in melanins by the cationic surfactants (527). 

The data for cuticle analysis are based on the work of Bradbury et al. [16] who analyzed cuticle and whole fiber from several keratin sources, including human hair, merino wool, mohair, and alpaca. These scientists concluded that there is very nearly the same difference between the amino acid composition of the cuticle and each of these fibers from which it was derived. They listed the average percentage differences used in these calculations. More recent analyses of cuticle and whole fiber of human hair [68, 69] are in general agreement with these data [18]. 

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 elemental composition of casein is not greatly different from that of wool (Table 10.13). The approximate amino acid compositions of each component phosphoprotein are listed in Table 10.14, their relative proportions in Table 10.12, and the casein amino acid sequences are indicated in Figures 10.22 through 10.25. These sequences are subject to minor variations particularly between animal species. Casein has numerous non-food applications (Chapter 12.17). 

There is evidence that little or no perceptible change in chemical nature, viz. disulfide group content, amino acid compositions, and oxidative main chain scission have occurred during graft copolymerization. Wool fibers can be specifically modified physically by grafting to break down hydrogen bonds in the a-helix. In such circumstances, a specific interaction may arise between... 

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. 

Table IL Amino Acid Composition of Wool Keratin (Molecular Weight 68,000 kD) (18,19)...

Changes observed in the amino acid composition of wool fiber proteins exposed to spontaneous microflora may testify that microorganisms degrade peptide and disulfide bonds, which provide stability of the primary stmcture of proteins, and break hydrogen bonds, which play the main role in stabilization of spatial stmcture of proteins (secondary, tertiary, and quaternary). 

The hair fibers derived from furry mammals are mainly made up (over 80%) of the structural protein keratin. The distinction between wool and hair is not compositional, but related to size wool fibers are generally fine and short, whereas those of hair are usually thicker and longer. The molecule of keratin consists essentially of a combination of amino acids about 18 amino acids make up the keratin molecule (see Textbox 67). The nature of the amino acids, their relative amounts, and their sequence and arrangement within the molecule of keratin vary from one animal species to another but are characteristic of any variety of wool or hair (Asquith 1977) (see Table 89). 

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