Entry of phosphate into yeast cell

Baker's yeast, Saccharomyces cerevisiae, has often been selected for study of active, or metabolically associated, salt accumulation. Particular attention has been devoted to the esterification of phosphate in this process and to the nature of coupling with a source of energy. The accumulation of phosphate has been considered as coupled to: A, the general reactions of glycolysis (10); B, the action of glyceraldehyde-3-phosphate dehydrogenase (6,16); C, a redox pump (4,5) and D, oxidations in the respiratory chain under aerobic conditions (14). With these concepts in mind, the manner of phosphate entry into yeast was examined by the methods of quantitative enzyme kinetics applied by C. E. Hagen and his associates (7) to analysis of phosphate entry into barley roots. The initial objective was to compare phosphate accumulation by Baker's yeast and barley roots, particularly with respect to aerobic and anaerobic conditions, in the hope of more clearly understanding the aerobic requirement of barley roots. Results obtained indicate that phosphate entry into yeast is coupled with three distinct reactions of oxidative phosphorylation, one of which is aerobic and the other two anaerobic.