SUMMARY: The dermatophyte, Microsporum canis, synthesized a complex of proteolytic enzymes localized in discrete organelles in the mycelium. On induction by protein in the growth medium, the intracellular level rose sevenfold and the enzymes appeared in the culture medium. The process is thought to be true secretion since an autolytic marker enzyme was present in insignificant amounts during the exponential growth phase when the proteases appeared. Amino acids in the medium repressed the synthesis of extracellular proteases.
The protease complex had pH optima at 6·6,8·0 and 9·5 to 10·0 and showed endo-peptidase rather than exopeptidase activity. The possible relevance of such an enzyme system to the pathogenicity and keratinophilia of Microsporum canis is discussed.
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