Nature of Particles Involved in Lipid Synthesis in Yeast.

Klein, Harold P. (Ames Research Center, Moffett Field, Calif.). Nature of particles involved in lipid synthesis in yeast. J. Bacteriol. 90:227-234. 1965.-Mitochondria-free homogenates of Saccharomyces cerevisiae yielded several particulate layers upon centrifugation at 100,000 x g. Electron microscopy revealed that membranes are present only in the uppermost ("fluffy") layer, which is inactive in lipid synthesis. The membrane-free material of the middle ("red") layer stimulated the synthesis of fatty acids and of nonsaponifiable lipids. In addition, this fraction appeared to be rich in the enzyme systems responsible for desaturating fatty acids and for converting squalene to sterols. The purified particles contained protein and ribonucleic acid (approximately 65:35), and further resembled ribosomal material in that they sedimented almost entirely as an 80S particle in tris(hydroxymethyl)aminomethane-magnesium buffer. Various treatments that dissociated the 80S material did not affect the lipogenic capabilities of this particle fraction.