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SUMMARYThe nets produced by protoplasts of Saccharomyces cerevisiae in liquid culture media consisted of microfibrils about 20 nm wide, forming flat, fairly straight bundles of variable width and length, up to about 500 nm wide and 4 pm long. Ends of microfibrils were seldom found. They were not attacked by chitinase or dilute acids, but the net structure disappeared in 3 % (w/v) NaOH, leaving about 60 % dry wt of the nets as-partly microfibrillar clusters. The X-ray powder pattern from the nets, in contrast to that from normal walls, exhibited a set of well-defined rings which identified two micro-crystalline constituents : chitin and unbranched chains of /3-(1+ +linked D-glucose residues. These latter were the alkali-soluble fraction. The X-ray diagram of the glucan, corresponding to that of paramylon, indicated an in vivo crystal modification. Up to 15 % dry wt was chitin which was formed de novo by the protoplasts.A fine net structure of microfibrils about 7.5 to 10 nm thick with meshes about 20 to 60 nm wide was demonstrated in normal walls, forming the entire inner layer and consisting mainly of yeast glucan. This glucan and chitin were only slightly crystalline in these walls. The features of the glucan and chitin of the protoplast nets indicate that enzymes active in normal wall formation were differentially removed or inactivated by the liquid medium.

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