The Structure and Chemistry of Human Hair 24 intermediate filament proteins from other types of tissue.54 Since that time, and now using gene techniques for identifying and amino acid sequencing, 11 type I and 6 type II intermediate filament proteins have been discovered in human hair.55 Coupled with this a new systematic nomenclature for the proteins was established (Appendix A).56 Figure 12 illustrates the amino acid sequence of a type I KIF protein from human hair (Ka36 now renamed K4056) published by MA Rogers et al. in 2004.57 For ease of understanding the various structural facets of this typical KIF protein, it is presented here in a form originally used in 1986.53 The protein contains 431 amino acids with each type labeled by letter according to convention (see Table 2). The molecule extends in a continuously connected fashion from the amino end of the protein at top left to the carboxyl end at bottom right of the diagram. The two ends of the molecule (shown as blocks of four columns width) contain sequences of amino acids associated with a random-coil tertiary structure and notably rich in cystine (C) as compared with other parts of the molecule. Between these are blocks labeled 1A, 1B, 2A and 2B containing amino acid sequences of a type associated with an α-helix. The amino acids in each of these blocks are shown as repetitive heptads in columns labeled a-to-g and the reason for this is that amino acids in columns a and d are predominantly hydrophobic in character. Heptad repetition of this type is a fundamental feature of proteins that form α-helical coiled-coils. In block 2B there is a stutter in the heptad sequence that can be accommodated in the hair IF coiled-coil structure with minor local distortion58 L1, L12 and L2 are random coil linker segments between the relevant α-helical rod-like structures. The overall general structure of type-II KIF proteins from human hair is similar to that for the type-I protein shown in Figure 12. Type I and type II proteins in human hair and other mammalian keratin fibers occur as pairs of equal amount. The charges along the lengths of the two molecules are complimentary and this dictates their parallel in-register amalgamation in the form of a two-stranded coiled coil.59 It is here the importance is revealed