STUDIES ON THE OXIDATIVE METABOLISM OF SACCHAROMYCES CEREVISIAE

Abstract

Vegetative cells of Saccharomyces cerevisiae were fixed with potassium permanganate followed by uranyl nitrate, embedded in methacrylate, and studied in electron micrographs of thin sections. Details of the structure of the cell wall, cytoplasmic membrane, nucleus, vacuole, and mitochondria are described. Cell membranes, about 70 to 80 A thick, have been resolved into two dense layers, 20 to 25 A thick, separated by a light layer of the same dimensions, which correspond in thickness and appearance to the components of the "unit membrane" as described by Robertson (15). The cell wall is made up of zones of different electron opacity. Underlying the cell wall is the cytoplasmic membrane, a sinuous structure with numerous invaginations. The nucleoplasm, often of uneven electron opacity, is enclosed in a pair of unit membranes in which nuclear pores are apparent. The vacuole, limited by a single unit membrane, is usually irregular in outline and contains some dense material. Rod-shaped mitochondria, 0.4 to 0.6 g in length and 0.2 to 0.3 g in diameter, are smaller in size, but similar in structure to some of those described in plant and animal cells. Attempts to use osmium tetroxide as fixative were unsuccessful, a result similar to that obtained by other workers. It is suggested that yeast cells are impermeable to osmium tetroxide, except when grown under specific conditions.

STUDIES ON THE OXIDATIVE METABOLISM OF SACCHAROMYCES CEREVISIAE

“…The low a-ketoglutarate dehydrogenase activity of the mitochondria described herein has not been suggested by earlier studies of such particles (15,23). Linnane and Still (15) have described a crude yeast mitochondrial fraction which oxidized acetate only in the presence of a-ketoglutarate as a "sparker," presumably involving the conversion of acetate to acetylCoA by a transacetylation reaction between succinylCoA and acetate.…”

“…Linnane and Still (15) have described a crude yeast mitochondrial fraction which oxidized acetate only in the presence of a-ketoglutarate as a "sparker," presumably involving the conversion of acetate to acetylCoA by a transacetylation reaction between succinylCoA and acetate. On the other hand, crude mitochondrial fractions prepared by Vanderwinkel et al (23) converted acetate directly to acetylCoA and oxidized it via the citric acid cycle. An extreme case of mitochondrial variation is seen with the mutant "petite" yeast described by Ephrussi and associates (6).…”

“…Attempts have been made in the past to isolate yeast mitochondria, and cell-free particles capable of terminal oxidation and some phosphorylation have been described (18,22). The isolation of mitochondrial fractions catalyzing the oxidation of the citric acid cycle substrates has also been reported (15,23), but the rates of the enzymatic activity indicated that those fractions probably contained some particulate material other than mitochondria.…”

The Biogenesis of Mitochondria

“…Mitochondria were prepared b>' the method of VitoLs and Linnane (1961) from cells disnipted by homogenization with ballotini glass beads.…”

“…1957;Linnane and Still, 1955;Utter, Keech and Nossal. 1958;Vitols, North and Linnane, 1961;Vitols and Linnane, 1961;Olinishi and Hagihara, 1964). Since the initial report by Ephrussi et al (1956) there have been many descriptions of the over-all changes in rt'spiralory aetivity and enzyme composition of whole yeast cells which result from growth on substrates (such as lactate or galactose) which permit high respiratory activity to develop, and on glucose whieh represses respiratory enzyme formation liy the yeast cell (Strittmatter.…”