Biochemical Studies on the Thermal Dimorphism of Paracoccidioides brasiliensis

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Abstract
The biochemical and morphological changes of the yeastlike (Y) form to the mycelial (M) form of Paracoccidioides brasiliensis were examined. The main polysaccharide of hexoses of the Y-form cell wall was α-glucan, whereas the polysaccharides of the M-form cell wall were β-glucan and galactomannan. The α-glucan of the Y form contained mainly α-(1 → 3)-glycosidic linkage. The β-glucan of the M form contained mainly β-(1 → 3)-glycosidic linkage with a few branches at C-6 position. The incorporation of 14 C-glucose into the cell wall glucans showed that synthesis of α-glucan decreased rapidly after the temperature of the culture was changed from 37 to 20 C. The synthesis of β-glucan was augmented at an early stage of the morphological change. The M-form cell wall contained 12 times more disulfide linkage than the Y form. The cell-free extracts of the whole cell of the Y form had five times more protein disulfide reductase activity than the M form, whereas extracts of the M form contained five to eight times more β-glucanase activity than the Y form. From these results, a hypothesis for the production of the M form from the Y form is proposed.