Isolation and chemical analyses of the cell walls of the yeast (Y form) and mycelial forms (M form) of Paracoccidioides brasiliensis and Blastomyces dermatitidis revealed that their chemical composition is similar and depends on the form. Lipids, chitin, glucans, and proteins are the main constituents of the cell walls of both forms of these fungi. There is no significant difference in the amount of lipids (5 to 10%) and glucans (36 to 47%0) contained by the two forms. In both fungi, the Y form has a larger amount of chitin (37 to 48%) than the M form (7 to 18%c), whereas the M form has a larger amount of proteins (24 to 41 %c) than the Y form (7 to 14%). Several properties of the glucan of P. brasiliensis were studied. Almost all of the glucan in the Y form was soluble in 1 N NaOH, was weakly positive in the periodic acid-Schiff reaction, was not hydrolyzed by snail digestive juice, and had a-glycosidic linkage. Glucans of the M form were divided into alkali-soluble (60 to 65%c) and alkali-insoluble (35 to 40%) types. The alkali-soluble glucan was similar to that of the Y form; the alkali-insoluble glucan was positive in the periodic acid-Schiff reaction and was hydrolyzed by snail digestive juice.

Glucans were isolated from the cell wall of the yeast (Y) and mycelial (M) forms of Paracoccidioides brasiliensis. The alkali-soluble glucan of the Y form had properties of a-1, 3-glucan. The alkali-insoluble glucan of the M form was identified as a /3-glucan which contains a ,B-(1-3)-glycosidic linkage by infrared absorption spectrum, by effect of j3-1 ,3-glucanase, and by partial acid hydrolysis. The alkalisoluble glucans of the M form were a mixture of a-and 3-glucans and the ratio of a-to f,-glucan was variable, depending on the preparations.

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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.