Keratin decomposition by dermatophytes. I. Sulfite production as a possible way of substrate denaturation

Abstract

The dermatophyte Microsporum gypseum was grown on children's hairs in a mineral solution. During the growth of the fungus the substrate digestion, pH of the medium, and concentrations of soluble decomposition products were determined. In aerated and stationary cultures the substrate digestion attained was 56% and 37 to 45%, respectively. The decomposition was accompanied by the alkalinization of the medium and by the release of peptidic substances.The average content of sulfur amino acids in soluble decomposition products was always lower than their content in keratin. Sulfhydryl compounds (cysteine) were found in traces only. The final product of the cystine metabolism was the sulfate excreted in high amounts into the medium. Sulfides, thiosulfates, and free sulfite were not present. However, after the treatment of the culture filtrates with cyanide, arsenite or cysteine well determinable amounts of sulfite were liberated. These reactions are typical of S‐sulfocysteine.The author presents the hypothesis that the dermatophytes can produce not only sulfate, but also sulfite in the course of keratinolysis. By the latter compound, disulfide bonds of the substrate could be cleaved to cysteine and S‐sulfocysteine. The keratin denatured by “sulfitolysis” would then be easily attacked by the proteases of the fungus.