Chemical Constitution of Keratin

Abstract

Wool fibres show histological structure when examined microscopically, and this structural heterogeneity has recently been shown in greater detail by the electron microscope^1,2,3. Apart from some analyses on scale substance by Geiger⁴, little chemical evidence on the composition of the different histological components is available. Recently, I have found that wool which has been deamidated by treatment with cetyl sulphonic acid⁵ (0.05M, 65°, 61/½ days) will partially disperse if stirred in dilute alkali (pH c. 11, room temperature, overnight), leaving a suspension of the resistant residues of the scales and cortical cells. When the clear alkaline supernatant liquor is acidified to pH 4–5, a protein-like material is precipitated which is soluble in either dilute acid or alkali. A fairly complete amino-acid analysis of these components has been carried out and is given in the accompanying table together with data for the intact wool from which they were derived. A is the resistant component of the scales and cortical cells, B is the portion precipitated from the alkaline liquor, while Aa is the resistant residue from retreatment of part of A with cetyl sulphonic acid followed by dilute alkali. These analyses show quite clearly a great difference in amino-acid composition between A and B and the intact wool. The general tendency is for amino-acids of high molecular weight to be concentrated in the soluble component, while the resistant component is particularly rich in cystine and proline. The results thus show great similarities to those of Geiger⁴, who probably analysed the resistant component of the scales.