Cell membrane complex epicuticle

The structure and degradation of the cell membrane complex including the structure of the epicuticle. 

A proteinaceous substance called epicuticle has been isolated from wool fiber by Golden et al. [73], The protein portion of this cell membrane complex material was found to be rich in the dicarboxylic amino acids, aspartic acid, and glutamic acid. 

Holmes [74] has isolated a fatty-acid protein complex from human hair that appears to protect the hair during papain digestion (cell membrane complex). Analysis of this complex indicates 20 to 30% fatty acid (lipid material) and 60 to 70% protein, rich in the amino acid lysine. Holmes suggests that this substance is either epicuticle or a fraction of the epicuticle. To avoid confusion, this material should be called either cell membrane complex or a portion of the cell membrane complex, which consists of protein and lipid components. 

The dissolution or the removal of structural lipids or proteinaceous matter from hair-probably from the cell membrane complex or epicuticle by either shampoos, surfactant solutions, or other cosmetic treatments-has been demonstrated by several different scientists. For example, Marshall and Ley [153] demonstrated the extraction of proteinaceous components from the cuticle of wool fiber by surfactant solutions of sodium dodecyl sulfate, cetrimonium bromide, and triton X-100. Zahn and co-workers [154, 155] and Mahrle [156] independently showed that part of the lipid components of the cell membrane complex were removed from hair by permanent waving. 

Morphologically, the fibres are composed of the cortex and the cuticle. Each of the two components is formed of various other morphological components (Table 9.6.3). The cortex contains cortical cells and the cell membrane complex. The cortical cell is further composed of macro-fibrils and intermacro-fibrillar material. The macro-fibrils consist of micro-fibrils and intermicro-fibrillar matrix. In summary, the cortex is formed of micro-fibrils (intermediate filament, IF, or keratin proteins, KP) and keratin associated proteins (IFAP or KAP), which compose the intermicrofibrillar matrix containing cytoplasmatic and nuclear remnants. This ensemble is wrapped up in the cuticle, as an external sheath which also has its own architecture, being formed of four layers the epicuticle, the a-layer, the exocuticle and the endocuticle. 

Wool fibers contain two types of cells, viz. cuticle cells and cortical cells. The cuticle cells consist of external epicuticle, exocuticle, and endocuticle. The cortical cells are divided into two different types of cells termed as orthocortical and paracortical cells which occupy about 90% of the wool fibers. They are separated from one another by a cell membrane complex with three layer structure. The cortex structure is constituted from the crystalline microfibril of the a-helical aggregate embedded in a matrix of high sulfur content. Wool fiber is thus a composite material with a variety of function on mechanical, chemical, and physical properties. 

The complex morphology of hair essentially consists of four components of different functionality (i) The cortex that gives the hair its mechanical properties consists of elongated, spin-shaped cells aligned in the direction of the fiber axis. The keratinized protein in the form of microfibrils resides in these cells, (ii) The medulla is located in the center of some thicker fibers and it consists of a loosely packed porous cellular structure (it does not contribute to the mechanical properties of the hair), (iii) Cell membrane complex which cements the various cells of the cuticula and the cortex and it consists of several layers, (iv) Cuticle, a multilayered structure which consists of flat cuticle cells and the most outer layer, i.e. the epicuticle (which is about 2.5 nm thick) is the most important part for deposition of surfactants and polymers in the shampoo formulation. This consists of 25 % lipids and 75 % protein, the latter having an ordered possibly p-pleated sheet structure with 12% cystine. The cystine groups are acylated by fatty acids which form the hydrophobic surface region. A schematic representation of the epicuticle is shown in Fig. 1.46. 

The fiber surface is bounded by a thin membrane 100 A thick called the epicuticle. The cuticle is a scaly, tubular layer and consists of flattened cells which overlap to give a rachet-like profile to the fiber. Each scale cell contains two distinct layers, a keratinous outer layer termed the exocuticle and a nonkeratinous inner layer that appears to be derived from cytoplasmic debris and is termed the endocuticle. There is some evidence that the exocuticle itself is complex with an outer cystine-rich layer termed exocuticle a. In coarse fibers the cuticle may be many scale-cells thick and where the cells overlap they are separated by an intercellular layer formed during biosynthesis by the deposition of nonkeratinous protein between the cell membranes. This layer is sometimes referred to as intercellular cement. 

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