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Extracellular proteolytic enzyme activity of Histoplasma capsulatum var. duboisii
F A Muotoe-Okafor1, H C Gugnani, O O Obidoa
1Department of Applied Microbiology, Nnamdi Azikiwe University, Akwa, Nigeria.
Abstract:
Histoplasma capsulatum var. duboisii is the etiological agent of African histoplasmosis, an important deep mycosis in West Africa. Not much is known about the physiological properties of this fungus. This communication reports on the extracellular proteolytic enzyme activity of this fungus. Five isolates of this fungus tested hydrolyzed azocasein and bovine serum albumin at pH 6.8 and 8.0. Assay of the crude enzyme showed that proteolytic activity increased with age and peaked on the 10th day and then again on the 13th day for the yeast form, and on the 11th day of growth for the mycelial form. The optimum temperature and pH for maximum enzyme activity were 35 degrees C and 6.8 respectively. The proteinase activity was more pronounced with the yeast form than with the mycelial form. The action of enzyme inhibitors suggested the presence of an aspartyl proteinase.
Insights
African histoplasmosis is caused by Histoplasma capsulatum var. duboisii. This study investigates its extracellular proteolytic enzyme activity, finding optimal conditions and identifying potential aspartyl proteinase characteristics.
Area of Science:
- Mycology
- Biochemistry
- Infectious Diseases
Background:
- African histoplasmosis, a deep fungal infection prevalent in West Africa, is caused by Histoplasma capsulatum var. duboisii.
- Limited information exists regarding the physiological characteristics of this fungal species.
Purpose of the Study:
- To investigate the extracellular proteolytic enzyme activity of Histoplasma capsulatum var. duboisii.
- To characterize the optimal conditions for enzyme activity and identify the enzyme type.
Main Methods:
- Five isolates of Histoplasma capsulatum var. duboisii were cultured.
- Extracellular proteolytic activity was assessed using azocasein and bovine serum albumin hydrolysis.
- Enzyme activity was measured over time, and optimal temperature, pH, and inhibitor effects were analyzed.
Main Results:
- All five isolates demonstrated extracellular proteolytic activity against azocasein and bovine serum albumin at pH 6.8 and 8.0.
- Proteolytic activity peaked on day 10 and 13 for the yeast form and day 11 for the mycelial form.
- Optimal enzyme activity occurred at 35°C and pH 6.8, with higher activity observed in the yeast form. Inhibitor studies suggested the presence of an aspartyl proteinase.
Conclusions:
- Histoplasma capsulatum var. duboisii possesses significant extracellular proteolytic enzyme activity.
- The yeast form exhibits greater proteinase activity than the mycelial form.
- The enzyme is likely an aspartyl proteinase, offering insights into the fungus's physiology and potential virulence factors.