The chemical composition and structure of the cell wall of Chlorella pyrenoidosa

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Abstract
A cell-wall fraction of C. pyrenoidosa was isolated after disin-tergration of whole cells in a Mickle cell disintegrator followed by differential centrifuging. The isolated wall, is approximately 210A thick and represents 13.6% of the dry weight of the whole cell. A quantitative chemical analysis of the wall was made with respect to the following fractions: a-cellulose, hemicellulose, protein, lipid and ash. Glucosamine has been estimated. The structure of the wall, studied by the electron microscope, was shown to be a 2-phase system in which microfibrils approximately 30-50A in diameter are enclosed in a continuous matrix. The protein, some of which may exist as a glycoprotein, is associated with the hemicellulose and with these polysaccharides makes up the greater part of the continuous matrix. The microfibrillar structure, which is nearly all polysaccharide, corresponds to the cellulose of the chemical analysis. It is composed of polymers of glucose, galactose, mannose, arabinose and rhamnose. The hemicellulose can be isolated as an electrophoretically pure polysaccharide from the whole cell and some of its characteristics were studied quantitatively. An acid hydrolysate contains galactose, mannose, arabinose, xylose and rhamnose. The microfibrils are present as a continuous irregular network over the cell wall and throughout its thickness. They lie approximately in 2 directions at right angles to one another. The continuous matrix is granular in appearance. Microscopical examination and chemical analysis of cell walls treated with snail digestive enzyme show that some of the substances of which they are composed are partially localized in 2 regions. One of these is near the outer surface and the other near the inner surface of the wall.