Variations in the Proteins of Wool and Hair

Summary

Keratins are not materials of unique amino acid and protein composition. A wide range of compositions over which satisfactory structure-function is achieved has been found; for example the half-cystine content of wool falls in the range 8% to 15%, and that of tyrosine 2.3% to 4.6%. Variations in composition occur not only between fibres from different individuals of a species but also along the length of fibres from the one animal. Protein composition may be influenced by the genetic origin, nutritional status and physiological state of the animal.

A major contributory factor to the variation in wool composition from sheep in the same flock is the genetic expression of the constituent wool proteins. Polymorphism amongst the intermediate filament (IF) wool proteins has not been found so far, but about 10% of human hair samples contain an additional IF protein. Considerable polymorphism has been found in the matrix high-sulphur proteins from wool, mohair/cashmere and human hair.

After wool growth is temporarily stopped by the administration of various compounds, for example cyclophosphamide, mimosine or epidermal growth factor, the early regrowth wool has an increased content of high-sulphur proteins and virtually no high-tyrosine proteins. As well, there is a marked decrease in the amount of an unusual protein rich in half-cystine and serine.

In healthy humans, it is unlikely that any significant variation in the proteins of hair will result from normal changes in nutrition. Physiological control has not yet been observed in the synthesis of the proteins of human hair.