The effect of oxygen concentration on the growth and metabolism of Saccharomyces cerevisiae grown with excess of potassium or in potassium-deficient media.

1. Saccharomyces cerevisiae cells grown in limiting K(+) concentration have their growth inhibited by O(2) concentrations above 40%. With these conditions the cells grow very large and are unable to maintain ionic gradients when washed with water. 2. Cells grown in excess of K(+) showed the same pattern of change in cell size with change in O(2) concentration, but the magnitude of the changes was much less. Cells grown in excess of K(+) were not leaky. 3. Cell death, growth and development of ;leakiness' were not correlated in the cells grown in limiting K(+) concentration. 4. The activities of both alcohol dehydrogenase and cytochrome oxidase were higher in K(+)-deficient cells than in the cells grown with excess of K(+). The differences were much larger when the measurements were made on a cellular basis than when made on a protein basis. 5. In 100% O(2) 3mm-K(+) in the medium was sufficient to produce normal yeast cells.