Extracellular acidification bySaccharomyces cerevisiae in normal and in heavy water

Abstract

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