FIG. 1.

Transport of l-malic acid by S. cerevisiae expressing or not expressing the MAE1 gene. The initial extracellular concentration of total l-malic acid was 16.6 mM in 0.1 M K₂PO₄ buffer, pH 3.5. ○, V5 YEp strain in the presence of 10 mM glucose; ▴, V5 YEp MAE1 strain without glucose; ●, V5 YEp MAE1 strain in the presence of 10 mM glucose. The dependence of malate uptake on PMF was determined by adding ionophores at the beginning of the transport assays. ⧫, V5 YEp MAE1 strain in the presence of 10 mM glucose and 100 μM CCCP; ■, V5 YEp MAE1 strain in the presence of 10 mM glucose and 1 μM valinomycin.