Dimorphism in Benjaminiella poitrasii: Involvement of intracellular endochitinase and N-acetylglucosaminidase activities in the yeast-mycelium transition

The chitinase and N-acetylglucosaminidase activities in cell-wall-bound and free fractions in the dimorphic fungus Benjaminiella poitrasii were studie d as a function of morphological (unicellular yeast-mycelium) transition. T he specific activities of chitinases of cell-wall-free, particularly in the membrane fraction, were significantly different in the yeast and mycelial forms. During the yeast-mycelium transition, the N-acetylglucosaminidase ac tivity isolated in a membrane preparation increased steadily. The activity of the yeast cells (0.83 +/- 0.17 nkat/mg protein) increased 17-fold to 14. 2 +/- 1.7 nkat/mg protein in 1-d-old mycelial cells. The endochitinase acti vity increased 12-fold between 6 and 12 h and thereafter practically remain ed unchanged up to 24h. A reverse trend in the chitinolytic activities was observed during the mycelium-yeast transition. Isoelectrofocussing (pH rang e 3.5-10) of mixed membrane fraction free of particulate fraction of parent and morphological (Y-5, yeast-form) mutant cells separated endochitinase a nd N-acetylglucosaminidase activity into two pH ranges, viz. 4.3-5.7 and 6. 1-7.7, respectively. The predominant N-acetylglucosaminidase activity obser ved at pH 6.9 and 7.1 for the parent strain membrane fraction was undetecte d in the mutant preparation. The results suggested that the membrane-bound (either tightly or loosely) chitinolytic enzymes, particularly, N-acetylglu cosaminidase, significantly contributed to the morphological changes in B. poitrasii.