An elastic network of the matrix phase of wool Ðbres is formed by disulphide bonds between cysteine residues of the high-sulphur (HS) proteins of the matrix. To elucidate the pattern of the disulphide cross linking we applied 1H and 15N NMR spectroscopy to synthetic fragments of the HS proteins and also to the products of their oxidation by air. Two di †erent regimes, oxidation in solution and oxidation in bulk, were employed. In solution of the four-Cysresidue peptides, the sequential dipeptide Cys-Cys repeat (present two times in model peptide 1) and the pentapeptide Cys-Xxx-Pro-Yyy-Cys repeat (present in model peptide 2) were found to form intrarepeat disulphide bonds and not to form a network. In bulk the behaviour of the two repeats di †ers dramatically : the peptide with the Cys-Xxx-Pro-Yyy-Cys oxidizes to a network, but for the peptide with the Cys-Cys repeat the oxidation in bulk does not di †er from that in solution and, therefore, does not lead to network formation. The latter is the consequence of an exceptional propensity of the two adjacent cysteines of the dipeptide repeat to form a small intrarepeat cyclocystine loop which is much stronger than that of any other pair of the cysteines of the system. The formation of the cyclocystine loops e †ectively eliminates the potential of the Cys residues of the dipeptide repeat to serve as cross links of a network. A special structural function of the Cys-Cys repeat and its implications for the elasticity of the network of the matrix are discussed.
1998 Society of Chemical Industry.