Chapter 1 33 cyclocystine) is sterically unlikely. On the other hand, a disulphide cross-link between a cysteine residue and another cysteine four residues further along the chain is a possibility raised by these authors. Interestingly proline as residue Y introduces a fixed conformation of the protein chain at that point (as compared with the normal opportunity for free rotation about the bonds between other residues). Such is often the characteristic of the so-called protein β-turn stabilized by an intermolecular hydrogen bond. The possibility therefore exists that a local sequence of the type –Cys- X-Pro-Y-Cys- in part of a high sulphur KAP might determine the presence of a hydrogen bond and disulphide-cross-linked β-turn. Such -turns along the protein chain would produce a relatively compact structure with a series of kinks. Of course this is pure speculation as indeed is the conformation and purpose of all the KAPs. Conclusion Looking back to the 1959 paper by Professor George Rogers9 on studies of the internal structure of human hair with the transmission electron microscope, one might be forgiven for thinking little further progress has been achieved in the intervening time. Whilst Rogers’ work was certainly groundbreaking, since then we have actually learned much more about the protein composition of the various structures he identified. In this respect, it is worth mentioning the enormous progress made in molecular biology for not only the genetic identification of the hair’s proteins but also for determining their amino acid sequences. By the use of immunofluorescence methods it has also been possible to determine in which cellular compartments of the hair the proteins are located.48, 49 Much work has been undertaken to determine the internal organization of the hair’s intermediate filaments, yet there remains the dilemma as to whether the proteins there are in parallel or anti- parallel array. This issue remains to be resolved, as too the spatial organization of the protein dimers within the filaments and the precise relationship between the high-sulphur KAPs in the matrix