Saccharomyces cerevisiae was grown anaerobically in media with different concentrations of K(+) down to less than 1mm. Below 3.2mm the K(+) concentration limited the growth rate and yield. 2. Yeast extract was essential for maximum growth. The yield of cells when the medium contained 0.83mm-K(+) was only 30% of the yield with 90mm-K(+). 3. At the end of anaerobic growth the cells grown in 0.83mm-K(+) had a higher concentration of oxidative enzymes than cells grown in 90mm-K(+). 4. The cells grown anaerobically in 0.83mm-K(+) could adapt to aerobic conditions if K(+) was present in the adaptation medium, but not otherwise. 5. The enzyme pattern of the yeast grown aerobically in 0.83mm-K(+) was very similar to the anaerobically grown cells and did not change markedly after the glucose was consumed.
