Isolation of a keratinolytic proteinase from Trichophyton mentagrophytes with enzymatic activity at acidic pH.

A keratinolytic proteinase with enzyme activity at acidic pH was isolated from culture filtrates of Trichophyton mentagrophytes, a major pathogenic fungus of dermatophytosis. The molecular weight of the proteinase was estimated to be 41,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 38,000 by gel filtration. The isoelectric point was determined to be 3.9. The proteinase had a pH optimum of 4.5 for keratin and 5.5 for hemoglobin. This enzyme hydrolyzed the synthetic chymotrypsin substrate Suc-Ala-Ala-Pro-Phe-MCA (Km, 0.59 mM), and its activity was strongly inhibited by chymostatin. Previously reported proteinases from dermatophytes have had enzyme activities in neutral or alkaline pH; however, healthy skin has a weakly acidic pH. Thus, the purified proteinase which has an optimal activity at acidic pH and hydrolyzes skin constituents could be an important virulence factor in dermatophytosis.