Quantitative analysis of proton movements associated with the uptake of weak carboxylic acids. The yeast Candida utilis as a model.

A quantitative analysis of the proton movements associated with the initial uptake rate of weak short-chain carboxylic acids was developed in order to estimate proton/carboxylate symports stoichiometries. The yeast Candida utilis was used as a biological model and the deduced equations were applied on the elucidation of the proton/carboxylate symports stoichiometries of lactate, succinate and citrate in a strain of that yeast species at different pH values. At pH 5.0, the proton/lactate and the proton/succinate symport stoichiometry was 1:1. In the cases of the proton/lactate and proton/citrate symports it appears that the stoichiometry ratio increased with increasing extracellular pH.