Comparative characterization of proteolytic enzymes from Trichophyton gallinae and Trichophyton verrucosum

The proteolytic activities of culture filtrates and cell homogenates of Trichophyton gallinae and Trichophyton verrucosum were compared when the fungi were grown in the presence of a readily assimilable source of C and N (Sabouraud's broth) and a poorly assimilable source (mineral medium containing soluble keratin (KS) protein prepared from either chicken feathers or guinea pig hair). The proteolytic activity of T. gallinae was found to be located predominantly in the cell homogenate although this depended somewhat on the nature of the C and N source in the medium. Enzyme activity in T. verrucosum on the other hand was located in the culture filtrate. The use of KS as a substrate revealed only one peak of enzymatic activity which occurred at pH 7.0 in both fungi. In the case of T. gallinae the total proteolytic activity was not related to the fungal biomass but did depend on the nature of the substrate; poorly assimilable substrates (native feathers and hair) stimulated a higher enzymatic activity per unit biomass than readily assimilable Sabouraud's broth. In T. verrucosum, proteolytic activity was related to the fungal biomass and was highest in Sabouraud's broth which proved most suitable for growth of the fungus. On the basis of the findings with six different inhibitors of protease activity, it is concluded that the proteolytic enzymes of T. gallinae differ from those of T. verrucosum in terms of their metal-dependence and contained serine as part of the active centre.