JOURNAL OF COSMETIC SCIENCE 456 The method of Swift and Holmes (6) has been used by several different researchers to obtain proteinaceous matter believed to be partially derived from the CMC. This method involves dissolving matter from hair using papain with a reducing agent such as bisulfi te or dithiothreitol (DTT). Bryson (76) conducted a series of experiments from which he concluded that the laminated structure observed under the TEM following a 72-hour digestion of wool fi bers with papain and reducing solution (somewhat standard proce- dure) is not derived entirely from the CMC. Prolonging the digestion beyond 72 hours increased the number of laminated layers beyond what could be accounted for by the number of cortical cells in a fi ber cross section. Bryson concluded that the CMC lipids were rearranging with other proteins and peptides to form these laminated layers. Mass spectrometric analysis of the proteins of the digestion residue indicated that the majority of the protein component was papain, suggesting that the CMC lipids had rear- ranged with papain to form the laminated structures. Therefore, Bryson concluded that it is not possible to isolate pure proteinaceous CMC by papain digestion. These conclu- sions by Bryson are consistent with those of Swift and Bews (77), who concluded that although treatments of keratin fi bers with enzymes and reducing agents do cause separa- tion of cells, they could fi nd no evidence of dissolution of the cuticle CMC via critical electron microscopic examination of treated hair sections. Therefore, the value of this method for isolation of CMC proteins is limited because of contamination with papain. To repeat, the diffi culty in isolating pure cell membrane proteins and pure delta layer proteins that are free of extraneous proteins and proteins from other regions of the fi ber is the primary obstacle to our understanding of the composition and structures of the proteins of this important region of the fi ber and the reason that the composition of the CMC proteins is still not adequately characterized. Table V Proteins Extracted from Wool with Formic Acid and n-Propanol/Water Compared with the Allworden Membrane Amino acids Allworden membrane (30) Formic acid (50) n-propanol (51) CHCl3/MeOH (56) Asp 3 5.7 3.7 6.2 Glu 8.6 7.2 2.4 7.5 Thr 2.1 3.8 3.2 5.1 Ser 14.3 8.1 11.7 13.3 Tyr 0 12 16.4 3 Pro 4.2 4 5.2 6.4 Gly 23.8 19.2 25 11.9 Ala 3.2 5.2 2.2 8 Val 5.6 4.2 2.8 5.9 Ile 1.2 3.3 0.8 3.5 Leu 2.9 9.2 6.1 8.1 Trp Phe 0.4 5.2 7.8 3.6 His 0.2 1.2 0.7 1 Lys 4.5 4 0.8 2.7 Arg 2.5 6.2 5.2 4.1 Met 0 0.9 0.2 0.8 Cys 21.1 0.4 5.5 9 Totals 97.6 99.8 99.7 100.1

CELL MEMBRANE COMPLEX 457 CHEMICAL AND PHYSICAL ACTIONS ON THE CMC OF HAIR The covalently bound lipids of the CMC of the cuticle are sensitive to oxidation, reduction, and alcoholic alkalinity, while the lipid beta layers of the cortex are affected more by lipid solvents and free radical chemistry. The beta layers of the cuticle are more sensitive to nucleophilic attack by species such as the hydroperoxide anion and mercaptans, but the beta layers of the cortex, with their multiplicity of double bonds (oleic plus palmitoleic acids, plus cholesterol and cholesterol sulfate) and tertiary hydrogen atoms (cholesterol and cholesterol sulfate) are more sensitive to free-radical chemistry. On the other hand, the membranes of the CMC are resistant to oxidizing and reducing agents (78). Several of these chemical actions make the CMC more vulnerable to fracture, to cuticle fragmentation, and to the propagation of cracks through the cortex, as will be described in this section. There is evidence that a signifi cant amount of free lipid (not covalently bound to hair proteins) is in the beta layers of the cuticle and likely in all lipid layers of keratin fi bers (58). Since about 50% of free lipid in human hair is fatty acid, free lipid provides acidic groups to the hair surface and decreases the isoelectric point, as shown by Capablanca and Watt (63). As hair is exposed to repeated shampooing, blow drying, and rubbing, and to sunlight, changes occur on and in the surface layers. These changes involve removal of some free lipids by shampoos and photo-degradation of 18-MEA, disulfi de, and other functional groups, and consequently, fractures form in or between layers from bending, stretching, and abrasive actions. These actions expose “new” protein material and sulfur acids, primarily sulfonate groups, with an accompanying decrease in the free lipid content of the hair surface, thereby con- verting the virgin hair surface from a hydrophobic entity with little surface charge to a hydrophilic, polar, and negatively charged surface. The more the exposure of the hair to chemical and abrasive actions, the further from the root ends the more hydrophilic the hair becomes and the more polar and more negatively charged the surface becomes. DAMAGE BY SHAMPOOS AND CONDITIONERS The dissolution or the removal of structural lipids or proteinaceous matter from hair, primarily from the CMC or endocuticle, by shaking keratin fi bers either in surfactant solutions, shampoo solutions, or even water has been demonstrated by several different scientists. For example, Marshall and Ley (79) demonstrated the extraction of proteina- ceous components from the cuticle of wool fi ber by shaking wool fi ber in surfactant solu- tions of sodium dodecyl sulfate, a common surfactant in many shampoos. Gould and Sneath (80) examined root and tip end sections of scalp hair by TEM. This hair had never been chemically treated. Gould and Sneath observed holes or vacancies in the thin cross sections, and these holes were more frequent and larger in tip ends than in root ends. These scientists attributed these holes to damaging effects by shampooing involving the breakdown and removal of the non-keratin portions (CMC and endocuticle) of the hair, leaving the intercellular regions more susceptible to fracturing. One of the most common types of fractures in hair fi bers forms in the dry state, and it occurs in the cuticle–cuticle CMC between the upper beta layer and the adjoining delta layer (see Figure 2) and is called beta-delta failure (39). Gamez-Garcia (32) noted that the