Movements of protons coupled to glucose transport in yeasts. A comparative study among 248 yeast strains

In 248 strains representing 205 yeast species, changes in pH coupled to glucose addition were followed in unbuffered cell suspensions. Alkalinization of the external medium elicited by glucose, indicating a H+-glucose symport was observed in 34% of the strains, most of them belonging to the genera Rhodotorula, Hansenula and Candida. H+ uptake coupled to glucose transport was observed only after exhaustion of glucose in growth media. This observation was taken as an indication that, in general, the synthesis of H+-glucose symport is under the control of catabolite repression. Subsequently to the addition of glucose, in most yeasts (82%) acidification was observed. This ability is probably related to the creation of a proton-gradient across the plasma membrane and is generally distributed among yeasts.