The role of intracellular pH in the regulation of cation exchanges in yeast.

1. When yeast oxidizes propan-2-ol in the presence of KCl no uptake of K(+) occurs. 2. When propionate is added to suspensions containing propan-2-ol, or if the suspensions are bubbled with CO(2), a considerable uptake of K(+) occurs. 3. Maximum K(+) uptake occurs at a propionate concentration of 2mm. 4. The addition of 20mm-propionate to the suspension lowers the intracellular pH of the yeast from a resting value in the region of 6.2 to approx. 5.6. 5. When K(+) uptake is measured in the presence of 20mm-propionate, progressive changes in the rate of K(+) uptake and intracellular pH occur. The optimum rate of K(+) uptake occurs at an intracellular pH of 5.70. 6. The effect of both intra- and extra-cellular pH on K(+)-K(+) exchange was studied and an optimum rate was found at an extracellular pH of 5.35, the corresponding intracellular pH being 6.44. 7. When a Na(+)-loaded yeast oxidizes propan-2-ol in the presence of KCl, a steady efflux of Na(+) and influx of K(+) occurs. The addition of 10mm-propionate to the suspension markedly inhibited the Na(+) efflux but only slightly decreased the K(+) influx. 8. The effect of both extra- and intra-cellular pH on Na(+) efflux was studied with propan-2-ol and with glucose. The results can be best interpreted in terms of intracellular pH changes, and an optimum was obtained at approx. pH6.40.