Biochemistry of the skin

Keratins

The important molecules synthesized by the skin include keratin, melanin, collagen and glycosaminoglycans (GAGs).

Keratins are high-molecular-weight polypeptide chains produced by keratinocytes ( Fig. 4.1 ). They are the major constituents of the stratum corneum, hair and nails. The stratum corneum comprises 65% keratin (along with 10% soluble protein, 10% amino acid, 10% lipid and 5% cell membrane).

Keratin proteins are of varying molecular weight (between 40 and 67 kDa). Different keratins are found at each level of the epidermis, depending on the stage of differentiation. Epidermal keratin contains less cystine and more glycine than the harder hair keratin.

Melanins

Melanin is produced from tyrosine ( Fig. 4.2 ) in melanocytes and takes two forms (see also Ch 3 ):

• ●

  eumelanin , which is more common and gives a brown–black colour

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  phaeomelanin , which is less common and produces a yellow or red colour.

Most natural melanins are mixtures of eumelanin and phaeomelanin. Melanins act as an energy sink and as free radical scavengers, and absorb the energy of ultraviolet (UV) radiation.