JOURNAL OF COSMETIC SCIENCE 452 3.3. The isoelectric point of wool increased as the effectiveness of the solvent system increased, with the most effective lipid solvent providing wool with an isoelectric point of 4.5. These data show that the true isoelectric point of the surface proteins of wool fi ber is closer to 4.5 than 3.5 and that free fatty acids in the surface layers are an important and essential component of the surface of animal hairs. Thus, the more free lipid that is present in these surface layers, the lower the isoelectric point of keratin fi bers. Therefore, all free lipid is not totally removed and should not be totally removed from the surface layers by the shampooing of hair or surfactant scouring of wool fi ber. In addition, free fatty acids are important to the isoelectric point of animal hair fi bers. Furthermore, the amount of free lipid on the surface of hair fi bers will infl uence hair friction, surface energy, and a whole range of important properties, including the adsorption of surfactants and other ingredients onto human hair and wool fi bers. PROTEINS OF THE CMC The schematic in Figure 2 depicts cell membrane proteins and multiple layers of pro- teins in the delta layer of the cuticle–cuticle CMC analogous to the delta layer of the cortex (5,9). The structures and composition of the proteins of the CMC are still not adequately characterized. The primary reason for this gap is that it is extremely diffi cult to isolate proteins from only the cell membranes or only the delta layer, and this diffi - culty has been the primary obstacle to our understanding the composition and structure of the proteins of this important region of the fi ber, but nevertheless I will review this area in this section. To date, much more scientifi c attention has been given to the analy- sis of cuticle cell membranes than to those of the cortex therefore, I will begin this discussion on the proteins in the cuticle cell membranes. PROTEINS IN THE CUTICLE CELL MEMBRANES The proteins of the cuticle cell membranes are associated with the Allworden reaction (14) as described earlier. The membranous epicuticle supports 18-MEA and is attached to the A-layer on the top of cuticle cells and has been isolated by shaking animal hair fi bers dur- ing Allworden sac formation with chlorine water and has subsequently been analyzed for amino acids. Perhaps the most quoted and “reliable” amino acid analysis of the Allworden membrane has been provided by Allen and coworkers (30), summarized in Table III. Since the attachment of 18-MEA to hair proteins is through thioester linkages and the cuticle cell membrane protein is cross-linked by cystine bridges, Negri et al. (12) proposed that the lipid layer must be attached to an ultra-high sulfur protein (UHSP) that can pro- vide attachment sites at approximately 1-nm spacings along the top of its folded chains. Zahn et al. (31) have provided indirect evidence by a multiple regression technique for the presence of approximately 51% UHSP, 42% loricrin, and 7% involucrin in the All- worden membrane as analyzed by Allen et al. (30), that is, in the cuticle cell membranes of wool fi ber or the 13–15 nm of the hair fi ber surface underlying the F-layer or 18-MEA. See Table III describing the amino acid analyses of these and other important proteins adapted from the paper by Zahn, et al. (31). From the results of this work and from previous work on the cell envelope of stratum corneum by Steinert and Marekov (68) and Jarnik et al. (69), Zahn et al. concluded that

CELL MEMBRANE COMPLEX 453 loricrin and involucrin are most likely in the cellular envelopes of wool (CE wool) and thus of human hair (CE hair) and other animal hairs. Loricrin is the major component (60% to 80%) of the cornifi ed cell envelope of stratum corneum in most animals, and involucrin, which is rich in glutamine, has an almost ideal structure to provide cross- linking sites to other proteins via isopeptide bonds. Therefore, involucrin is likely a major component of the cuticle cell membrane. Isopeptide bonds are formed between glutamine and lysine, reacting in the presence of a transglutaminase enzyme similar to what Steinert and Marekov (68) have shown occurs in the cellular envelope of human skin. Exactly how these proteins might be arranged in the cuticle cell membranes is not known at this time. One reasonable conjecture is that two layers exist in the epicuticle, the outermost (upper) layer being comprised primarily of UHSP to provide anchoring sites for 18-MEA on the top portion of the membrane and also covalent anchoring sites for other fatty acids on the bottom part of epicuticle cells. Involucrin is likely interspersed in the UHSP to provide isopeptide crosslinks to it and also to loricin and other proteins in the second layer of the cuticle cell membrane. Zahn et al. (31) also pointed out that small proline-rich proteins (SPRP) that are rich in glu- tamine and lysine are also most likely a part of this membrane because SPRPs (70) have been shown to participate in isopeptide cross-linking in the CE of stratum corneum and Table III Amino Acids (in mole%) of Allworden Membrane vs Calculated Values for Wool CE by Zahn et al. (31) and Proteins Believed to Be Part of This Membrane Amino acids Wool CE Human loricrin Human involucrin Human UHSP Human SPRP Allworden membrane Asp 2.7 0.3 2.8 3.4 0 3 Glu 9.8 4.4 45.8 8.2 28 8.6 Thr 2.2 2.2 1.6 10.3 2.4 2.1 Ser 15 22.8 1.6 10.9 0.4 14.3 Tyr 0.2 2.5 0.8 1 0 0 Pro 4 2.9 5.7 9 31.2 4.2 Gly 24.5 46.8 6.7 5 0 23.8 Ala 3.2 1 1.5 1.4 0 3.2 Val 3.5 3.5 3.7 3.8 9.6 5.6 Iso 1.1 1.6 0.4 1.6 0 1.2 Leu 2.4 0 14.6 2.4 1.6 2.9 Trp 0 0.3 0 0 0 Phe 0.8 2.9 0.6 0.8 0 0.4 His 0.9 0.3 4.7 0.7 0.8 0.2 Lys 5.3 2.2 7.4 3.7 12. 8 4.5 Arg 1.7 0 0.7 5.6 0 2.5 Met 0 0 0.9 0 0 0 Cys 22.7 6 0.3 32.2 11.2 21.1 Totals 100 99.7 99.8 100 98 97.6 Wool CE calculated by Zahn et al. (31). Human loricin from Hohl et al. (64). Human involucrin from Eckert and Green (65). Human SPRP from Marvin et al. (66). Human UHSP from Tezuka and Takahashi (67). Allworden membrane by Allen et al. (30).