Chitin and a β-linked glucan were the major chemical components of cell walls. Other monomeric residues identified in enzymic and acid hydrolyses of whole cell walls and cell-wall fractions included galactose, mannose, glucuronic acid and galactosamine. The β-glucan contained (1 → 3) and (1 → 6) linkages and was two-thirds digested by an exo-β-D-1,3 glucanase prepared from a cell-wall lysing Streptomyces species. An α-glucan was identified as a cell-wall component and it also contained (1 → 3) linkages. This latter polysaccharide was distinguishable from nigeran (an α-1,3; α-1,4 glucan present in other Aspergillus species) by infrared spectroscopy and by its low susceptibility to hydrolysis by an endo-α-1,3; α-1,4 glucan glucanohydrolase. Both glucans were alkali-soluble, but the β-glucan was completely solubilized only after acid extraction of the wall. The -acetylglucosamine to galactosamine ratio in the cell wall was 1.32 and the two hexosamines were shown to be constituents of distinct polymers. The remaining cell wall was accounted for by protein, lipids, readily extractable and bound, and, in the wild-type, melanin.

The melanin was distributed throughout the cell wall but was associated particularly with the chitin fraction. The pigment has been partially characterized chemically and contains indolic residues; this result does not substantiate earlier views that indolic melanins are peculiar to the animal kingdom. Melanin appears to be a finite heteropolymer both in terms of its molecular size and its chemistry.


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