Nucleoprotein layer of the yeast cell

ELECTRON MICROSCOPY OF A FISSION YEAST, SCHIZOSACCHAROMYCES POMBE

Maclean, Norman (University of Edinburgh, Edinburgh, Scotland). Electron microscopy of a fission yeast, Schizosaccharomyces pombe. J. Bacteriol. 88:1459-1466. 1964.-The structure of the fission yeast, Schizosaccharomyces pombe, was studied electron microscopically, with potassium permanganate and osmium tetroxide as fixatives. The cell was found to be bounded by a cell wall, 1,000 to 2,000 A thick, and a cell membrane. A layer of material was found between the cell membrane and the wall. The central nucleus, 2 to 3 mu in diameter, was bounded by a nuclear membrane, seen in some pictures to be double. Osmium tetroxide fixation revealed a granular body within the nucleus, identified as a nucleolus. Cytoplasmic structures included numerous vacuoles (probably normally containing lipid), a number of membranes and vesicles (which may represent a poorly organized mitochondrial system), and numerous granules (probably representing ribosomes).

RELEASE OF NITROGENOUS SUBSTANCES BY BREWER'S YEAST. IV. ENERGETICS IN SHOCK EXCRETION OF AMINO ACIDS

Lewis, M. J. (University of California, Davis), and H. J. Phaff. Release of nitrogenous substances by brewer's yeast. IV. Energetics in shock excretion of amino acids. J. Bacteriol. 89:960-966. 1965.-When suitably grown yeast cells are suspended in a solution of fermentable sugar, amino acids from the internal pool are rapidly released from the cells, a phenomenon referred to as shock excretion. After approximately 2 to 3 hr, in the presence of excess sugar, the amino acids are almost completely reabsorbed. This observation has been further studied with particular reference to the energy-yielding reactions of the cell. It has been established that amino acid release increases more rapidly with a rise in incubation temperature than does fermentation rate. Amino acid release cannot be inhibited by the common uncouplers of adenosine triphosphate synthesis (azide, arsenate, or 2,4-dinitrophenol) at concentrations adequate to prevent reabsorption of amino acids-an energy-requiring event. Inhibitors which completely inhibit the dissimilation of glucose (such as iodoacetate and fluoride) or those preventing entry of glucose into the cell (uranyl acetate) are effective in preventing amino acid release. It was concluded that shock excretion of amino acids is independent of energy-yielding reactions, but may be the result of changes in the state of the cell contingent upon the continuous flow of a fermentable sugar across the cell membrane.

Demonstration of the polysaccharides in the cell wall of Candida albicans blastospores, using silver methenamine staining and a sequence of extraction procedures

Blastospores of Candida albicans were subjected to a series of extractions of increasing severity to remove polysaccharides from the wall. The procedure was observed by electron microscopy, using silver methenamine staining to localize the polysaccharides.

Surface structure of yeast protoplasts

The fine structure of the yeast cell wall during protoplast formation was studied by means of phase-contrast microscopy and the freeze-etching technique. The freeze-etching results indicated that at least in some cases the entire wall substance was not removed from the surface of the protoplasts. After a treatment of 30 min to 3 hr with 2% snail enzymes, an innermost thin wall layer as well as remnants of the fibrillar middle layer sometimes could be demonstrated.