8-7 



THE YEAST CELL 



crowded with stored materials, but chemical analysis (ether ex- 

 traction) revealed that only 6.16 per cent fat was present. The hy- 

 brid stored carbohydrate poorly. Nitrogen analyses were converted 

 to protein by multiplying by the factor 6.25 (Table 8-2). The sam- 

 ple was ashed, and the difference was estimated to be carbohydrate. 

 Table 8-3 reveals that the reserves of glycogen hindered the re- 

 spiratory and fermentative activity of the cells considerably. 



Before understanding the harmful effects of high sugar concen- 

 trations, we grew yeasts in a medium containing 8 per cent sugar, 

 peptone^ and yeast extract. In this medium 50 to 90 per cent of the 

 cells died, especially if the cultures were well -aerated. The dead 

 cells gave normal QcOz ^^^ QcOa values ranging from 300 to 450; 

 but with Q02 values of 0. The dead cells were unable to consume 

 O2, although they were able to ferment. Some of our dormant cul- 

 tures contained nearly 100 per cent viable dormant cells. These 

 viable dormant cells, loaded with reserve materials, were imable 

 to consume O2 or to evolve CO2, but their inability to consume O2 

 is obviously different from that of cultures containing many dead 

 cells. Death of the cell apparently destroys its ability to take up 

 O2 without affecting seriously its ability to ferment. 



The reproducibility of results obtained by the Warburg respiro- 

 meter depends upon the absence of accumulations of reserve ma- 

 terials in the cells. Cells should be aerated and transferred to the 

 Warburg apparatus when a. minimum number of dead cells is pres- 

 sent and a considerable proportion is actually budding. In order 

 to make reproducible analyses, growth must be stopped in an active 

 phase and the cells washed with M/15 phosphate. If the cells are 

 allowed to stand in a nutrient medium, they will accumulate some 

 reserve fat or carbohydrate, or both, depending on the aeration and 

 the concentration of sugar. 



Table 8-2 



Chenical Analyses of Cells Containing Visible De- 

 posits of Mitochondria and Glycogen Compared to Nortial 

 Cells 



