STRUCTURAL ASPECTS OF KERATIN FIBRES 439 50•o helix while high-sulphur SCMKB kerateines are almost completely devoid of helix (86). Partial digestion of the low-sulphur SCMKA fraction from wool gives rise to helix-rich material (87, 88). Using Davies' graphical method (89), Asquith and Shaw (90) have calculated that low-sulphur e-keratose contains 29•o (Val + Ile + Ser + Thr + Cys) and hence is about 40•o e-helix, and that high-sulphur I•-keratose contains 53}/0 (Val + Ile + Ser + Thr + Cys) and hence is non-e-helix. Although the helical regions of the low-sulphur SCMKA fraction contain most of the lysine residues of the wool fibre, they are highly anionic because they also contain most of the free carboxyl groups. The non-helical sections in the SCMKA fraction are cationic (88). From the amino acid composition and physical measurement data, it would appear that the low-sulphur fractions are derived from the proto- fibrils and the high-sulphur fractions from the intermacrofibrillar matrix. It is generally agreed that the protofibrils consist of several e-helical poly- peptide chains twisted around one another in a rope-like manner, and it is essentially this ordered structure which gives rise to the X-ray diffraction pattern of e-keratins. On this basis, the matrix protein is considered to be disordered, at least in so far as there is insufficient long-range order to give rise to an X-ray diffraction pattern. The matrix is more heavily stained by metals than the protofibrils and this would seem to indicate that the former contains more cystine. However, it is not yet possible to separate unequivo- cally the matrix protein from the protofibrillar protein, which is not sur- prising in view of the obvious difficulties involved. Thus, all evidence with regard to the identity of the proteins of the matrix and the protofibrils is of necessity indirect (6, 91). The fractionation and separation of a single protein molecular species from such a mixture has been the subject of extensive research. The work of Lindley, Gillespie and Haylett (92) on a protein from SCMKB-2 high- sulphur protein fraction shows the occurrence of a high frequency of homodipeptides such as Pro-Pro, Val-Val, Glu-Glu, and Cys(CH•CO•H)- Cys(CH•CO2H). By partial acid hydrolysis of [asS]-cystine labelled wool, the Cys-Cys sequence is shown to occur frequently (93). Asquith and co- workers (94) have also found that Cys(SOaH)-Cys(SOaH) is a very import- ant sequence in T-keratose, over 30•o of the cysteic acid occurring in this sequence, and thus have postulated that a large proportion of the lanthionine formed in wool under suitable conditions is intramolecular. Recently, a polypeptide containing 97 amino acid residues, of which 26 are aromatic (tyrosine and phenylalanine) and 24 are glycine, has also been

440 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS isolated from reduced wool and partially characterized by Zahn and Biela (95). For the first time the complete amino acid sequence of three homogen- eous proteins, isolated from SCMKB fraction of Merino wool, has been established by Haylett, Swart and co-workers (96). The S-carboxymethylated proteins have a molecular weight of 11 409 4- 150. They consist of single chains containing 97 or 98 residues. Their N-terminal sequence is Ac-Ala- Cys(CH•.CO•.H) and they have S-carboxymethylcysteine as C-terminus. The molecules can be divided arbitrarily at position 49 into high- and low- sulphur proteins but the amino acids that prevent helix formation, such as proline, serine, and threonine, are fairly evenly distributed throughout the molecules. These high-sulphur proteins therefore appear to have no helical content and are ideally suited for the function of matrix protein in wool. The work of Corfield, Fletcher and Robson (97) on a protein fraction, isolated in 365/o yield from oxidized wool, has led these authors to suggest that wool consists of only one main protein composed of relatively short helical regions interspersed with sequences rich in cystinc, proline, serine, and threonine residues. It is suggested that this fraction is derived from a protein that constitutes the major part of the cortex. Further evidence in this field may therefore provide direct chemical evidence regarding the validity of the concept of the two-phase two-protein theory. ACKNOWLEDGEMENTS The author is grateful to Professor R. S. Asquith and Dr. J. A. Swift for helpful suggestions and comments. Figs. 1-5 were kindly supplied by Dr. Swift. (Received: $rd January 1972) REFERENCES (1) Astbury, W. T. and Woods, H. J. X-ray studies of the structure of hair, wool and related fibres. II. The molecular structure and elastic properties of hair keratin. Phil. Trans. Roy. Soc. London. A232 333 (1933). (2) Pauling, L., Corey, R. B. and Branson, H. R. The structure of proteins: two hydrogen- bonded helical configurations of the polypeptide chain. Proc. Nat. Acad. Sci. U.S. 37 205 (1951). (3) Lundgren, H. P. and Ward, W. H. in Borasky, R. Ultrastructure of Protein Fibres 39 (1963) (Academic Press, New York). (4) Mercer, E. H. and Matoltsy, A. G. Keratin, in Montagna, W. and Dobson, R. L. Advances in Biology of Skin, Vol. 9, Hair Growth (1969) (Pergamon, Oxford). (5) Ward, W. H. in Alexander, P. and Lundgren, H. P. Analytical Methods of Protein Chemistry, Vol. 4, 185 (1966) (Pergamon, Oxford). (6) Crewther, W. G., Fraser, R. D. B., Lennox, F. G. and Lindley, H. The chemistry of keratins. Advan. Protein Chem. 20 191 (1965).