EXTRACELLULAR ACIDIFICATION BY SACCHAROMYCES-CEREVISIAE IN NORMAL ANDIN HEAVY-WATER

Titratable acidity of the extracellular medium was compared with that calculated from pH changes in a suspension of Saccharomyces cerevisiae . After addition of cells to normal water the ratio of titratable acid ity to the computed one was about 25, after addition of 50 mmol/L D-gl ucose it was about 13, after subsequent addition of K+ ions it was onl y 2. In heavy water the respective values were 30, 9, and 1. Apparentl y, the principal buffer-generating processes have to do with glucose m etabolism but little with the K+/H+ exchange observed after addition o f K+. D2O appears to block processes producing the buffering capacity of the medium, among them possibly extrusion of organic acids.