Peptidases of Dermatophytes

Abstract

The normal sites of dermatophyte infection are the keratin-containing tissues, hair, nail and epidermis; and these fungi are commonly considered to be keratin digesting organisms. However a keratin degrading system has never been isolated from them and little is known of the properties of their proteolytic enzymes. Micro-fungi which have been studied in more detail (e.g. Johnson and Peterson, (1), McConnell (2), Crewther and Lennox (3)), show the production of varying mixtures of endo- and exo-peptidases with activities spread over a wide range of pH values, and recorded observations on dermatophytes accord in general with this pattern. Fujii (4) showed peptidase activity in Trichophyton mentagrophytes between pH 5-9 while Cruickshank and Trotter (5) showed such activity to be maximal at about pH 7 and 10 in this organism and also in Trichophyton rubrum. The present paper presents a more detailed study of the variation of proteolytic activity with pH and substrate in representative strains of some dermatophytes together with attempts to separate and characterise various components of the crude extracted proteolytic system from T. rubrum and Trichophyton verrucosum var.dis-coides. MATERIALS AND METHODS Cultivation of Mycelium All strains were fresh isolates provided either by Dr. Jacqueline Walker or Dr. C. J. La Touche; they were maintained on peptone agar. Growth for purposes of enzyme extraction was in stationary culture in Sabouraud broth, with the addition of 0.1% Difco yeast extract for the growth of T. verrucosum var.discoides, the inoculum being a small amount of a mycelial homogenate. The mycelial mats were filtered on to Buchner funnels and well washed with distilled water. Large batches of mycelium were grown by Dr. J. C. Belton at the Ministry of Supply, Microbiological Research Station, Port on, Wilts., under the above conditions and then freeze dried before being sent to Leeds.