Distribution of Inositol in Subcellular Fractions of Yeast Cells

This research was prompted by the fact that inositol has been recognized as an essential yeast nutrilite for many years (Eastcott, 1928), yet it has no established rule in cellular physiology. Some investigators have postulated that the primary function of inositol is that of a building block for some structural component of the cell. This is based upon the observations that inositol is required for yeast growth in much larger amounts (5 to 10 mg per L) than other B vitamins and that it is known to be a component of certain types of lipids. Analysis of a variety of tissues has shown that inositol is present chiefly as a component of phospholipids (Wittcoff, 1951) and lipo-protein complexes (Folch and Le Baron, 1951). In cereal grains, inositol is found in large amounts of phy-tin, the calcium, magnesium salt of the hexaphos-phate ester. Analysis of yeast cells has shown that most of the inositol is present in a bound form which yields free inositol upon acid hydrolysis (Smith, 1951). Yarbrough and Clark (1957) have shown recently that 80 to 85 per cent of the bound inositol in Schizosaccharomyces pombe is lipid in nature. (However, only free inositol can be utilized for growth by inositol dependent yeasts.) (Woolley, 1941b). As part of a study of the role of inositol in the metabolism of yeasts we have determined the distribution of free and combined inositol in various subcellular fractions of yeast cells with the objective of defining more precisely its loca-tion within the cell, and its possible role as a structural component. Preliminary observations have also been made upon the nature of the combined forms of inositol in the yeast cell.