BIOCHEMICAL PROPERTIES OF SCHIZOSACCHAROMYCES POMBE DEPENDING ON CULTURE CONDITIONS AND ON ACTION OF INHIBITORS .I. STUDY OF PHOSPHOLIPIDS

The formation of phospholipids has been studied in cells of Schizosaccharomyces pombe treated with 13 growth inhibitors; 3 of these, isomytilitol, 2-C-methylene-myo-inositol oxide, and 2(4)-C-methylene-epi-inositol oxide, are competitive inhibitors of inositol. With the exception of cells treated with isomytilitol, and cells in hypovitaminosis, all the inhibited cells are characterized by a 4-5-fold increase in the quantity of inositol they contain. This inositol is present essentially in the form of monophosphoinositides, a fact which has been confirmed by direct analysis of the cell phospholipids from 8 types of culture. A much larger incorporation of inositol per mg cells is also seen in normal cells at the beginning of the logarithmic phase, in cells in hypervitaminosis, and in cells having a smaller growth rate due to an insufficient concentration of glucose in the medium. For a given initial concentration of inositol, the incorporation of the cyclitol increases, as the number of cells decreases. During inhibition by isomytilitol, an increase in cyclitol phospholipids is seen : the latter contain, in addition to normal quantities of phosphoinositides, considerable amounts of abnormal isomytilitol-containing phospholipids. It is known that cultures, strongly inhibited by 2-C-methylene-myo-inositol oxide, are partially deinhibited by isomytilitol; their morphology is then analogous to that of the cells treated with isomytilitol. It has been shown that the two types of cells are also identical with respect to the composition of their cyclitol phospholipids. While cells, inhibited by 2-C-methylene-myo-inositol oxide, are deinhibited by addition of further amounts of inositol, the quantity of inositol in the cells approaches more and more that found in cells in hypervitaminosis. The phosphoinositides found in this yeast appear to be a form of reserve inositol. There seems to be a limiting minimum amount of phosphoinositide necessary for cell division to take place. © 1969.