Epidermis amino acids

Feruloylated pectins have been found in the parenchymatous cell walls of many Dicotyledons (mainly in the Centrospermae and Solanaceae), but UV-fluorescence microscopy suggests that at least the epidermal cell walls of all Dicotyledons contain phenolic residues it remains to be seen whether these phenolic residues are attached to polysaccharides or to cutin, but location of even a small quantity of, say, feruloyl-pectin in the epidermal wall would be particularly significant in the control of growth because the extensibility of the epidermis controls the expansion of whole stems (23) and leaves (Fry, unpublished observations). The extensins, as already mentioned, are rich in the phenolic amino acid tyrosine (2). 

The most superficial layer of skin is the stratum comeum (SC), which consists of terminally differentiated keratinocytes (comeocytes) that originate from actively proliferating keratinocytes in lower epidermis (basale, spinosum, and granulosum cells), and contain a lamellar lipid layer secreted from lamellar bodies (Fig. 7a). Flydration of the SC is an important determinant of skin appearance and physical properties, and depends on a number of factors including the external humidity, and its structure, lipid/protein composition, barrier properties, and concentration of water-retaining osmolytes (natural moisturizing factors, NMFs) including free amino acids, ions, and other small solutes. 

Katagiri, C., Sato, J., Nomura, J., and Denda, M. (2003) Changes in environmental humidity affect the water-holding property of the stratum corneum and its free amino acid content, and the expression of filaggrin in the epidermis of hairless mice. J. Dermatol. Sci. 31 29-35. 

Tabachnick, J. and Labadie, J.H. Studies on the biochemistry of epidermis. IV. The free amino acids, ammonia, urea and pyrrolidone carboxylic acid content of conventional and germ free albino guinea pig epidermis, J. Invest. Dermatol., 54, 24, 1970. 

Amino acid Epidermis " Epidermis Normal callus Keratin B from normal callus- Psoriasis scales" Exfoliate dermatitis scales ... 

Active studies of the basic amino acids in the epidermis in the 1930 s sought to make a distinction between the hard keratin (eukeratin) of hair, horn, nails etc., and the soft keratin (pseudokeratin) of the epidermis, horse burrs, and whalebone (20). The results of independent workers like Block (19) and Eckstein (29) were in agreement in the case of pepsin- or trypsin-treated epidermis where the ratios of histidine lysine arginine residues were approximately 1 3 3. These results were in marked contrast to the earlier work of Wilkinson (57) who found a... 

At the time these estimates of the basic amino acids seemed a useful contribution to make. A classification of proteins as closely or distantly related is still a desirable goal, but it is fairly certain that proteins having basic amino acid ratios of 1 3 3 and 1 6 15 can be more closely related than two proteins which may both have the same ratio. The efforts did show that the enzyme-resistant protein in the epidermis differed from the similarly resistant protein of the hard keratins in containing relatively much less arginine. They also showed that the ratios for the whole structure did not differ significantly from the ratio for the very small residue left after enzyme treatment. A modern approach would attempt a complete analysis of all amino acids and preferably only on well defined protein species within these structures. 

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