Isolation of `Vacuoplasts' from Poterioochromonas malhamensis

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Abstract
A method is reported for the isolation of vacuoplasts from P. malhamensis. Vacuoplasts are separated mechanically by centrifugation of silica-sol gradients. They consist of the leucosin storage vacuole, a portion of the plasma membrane and some cytoplasmic components. This method is suited to give a high yield of vacuoplasts. Vacuoles are the largest membrane-bound organelles in plant cells. Only a few methods exist for their large scale isolation and purification in an intact and physiologically active state. The high shear forces used to disrupt cell walls during tissue fractionation usually also disrupt the fragile vacuoles. The wall-less flagellate P. malhamensis is a fresh water organism with 2 unequal flagellae, belonging to the order Chrysomonadina, a group whose members characteristically store oil and leucosin. Leucosin (= chrysolaminarin) is stored in a posterior vacuole, which may be so large as to almost fill the cell. Leucosin is a polysaccharide composed of .beta.-(1 .fwdarw. 3)-linked D-glucose residues. It has a degree of polymerizaton about 34, is water oluble, and probably has a slightly branched structure.