Metachromatic basophilia of keratin after oxidation-cleavage of disulfide bond.

Abstract

Oxidation of keratinous structures by peracetic acid, bromine in carbon tetrachloride, or neutral potassium permanganate produced an insoluble, strongly acid substance capable of taking up basic dyes even from pH 1.2 solution. Thus, hair shafts, nails, and, to a much less extent, stratum corneum of the epidermis were rendered basophilic and metachromatic. The oxidation product strongly resisted methylation, thereby differing from the basophil substance of cell nuclei, of mast cell granules, and of cartilage. Furthermore, the oxidation product was not blocked by aniline chloride or phenylhydrazine, indicating that aldehydes, if formed, were not responsible for the basophilia by the formation of Schiff's bases. Periodic acid (1% aqueous solution for 2 hours at 60°C.) also rendered keratinous structures basophilic but to a less intensity than with the other oxidizing agents. Chromic acid was ineffective under the conditions used and, moreover, largely destroyed nuclear basophilia. The various oxidizing agents that induced metachromatic basophilia in keratin have in common the property of cleaving the disulfide bonds of cystine, yielding cysteic acid. In the case of oxidized keratin, it appears that the resultant cysteic acid residues remain bound in peptide chains but still possess free sulfonic acid radicals. Since sulfonic acids are strong acids, such groups probably account for the observed metachromatic basophilia in oxidized keratinous structures.