title: A comparative study on the transport of L(-)malic acid and other short-chain carboxylic acids in the yeast Candida utilis: evidence for a general organic acid permease.
abstract: Cells of the yeast Candida utilis grown in medium with short-chain mono-, di- or tricarboxylic acids transported L(-)malic acid by two transport systems at pH 3.0. Results indicate that probably a proton symport for the ionized form of the acid and a facilitated diffusion for the undissociated form were present. Dicarboxylic acids such as succinic, fumaric, oxaloacetic and alpha-ketoglutaric acids were competitive inhibitors of the malic acid for the high-affinity system, suggesting that these acids used the same transport system. In turn, competitive inhibition uptake studies of labelled carboxylic acid in the low-affinity range indicated that this system was non-specific and able to accept not only carboxylic (mono-, di- or tri-) acids but also some amino acids. Additionally, under the same growth conditions, C. utilis produced two mediated transport systems for lactic acid: a proton symport for the anionic form which appeared to be a common monocarboxylate carrier and a facilitated diffusion system for the undissociated acid displaying a substrate specificity similar to that observed for the low-affinity dicarboxylic acid transport. The mediated carboxylic acid transport systems were inducible and subjected to repression by glucose. In glucose-grown cells the undissociated dicarboxylic acids entered the cells slowly by simple diffusion. Repressed glucose-grown cells were only able to produce both transport systems if an inducer, at low concentration (0.5%, w/v), was present during starvation in buffer. This process was inhibited by the presence of cycloheximide indicating that induction requires de novo protein synthesis. If a higher acid concentration was used, only the low-affinity transport system was detectable, showing that the high-affinity system was also repressed by high concentrations of the inducer.
authors.affiliation: Laboratory of Biology, University of Minho, Braga, Portugal.
authors.forename: F
authors.initials: F
authors.lastname: Cássio
authors.forename: C
authors.initials: C
authors.lastname: Leão
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002175:Candida / Q000201:enzymology / Q000378:metabolism*; D002264:Carboxylic Acids / Q000378:metabolism*; D003998:Dicarboxylic Acids / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008293:Malates / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D015203:Reproducibility of Results; D013379:Substrate Specificity; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D014233:Tricarboxylic Acids / Q000378:metabolism
chemical_list: D002264:Carboxylic Acids; D003998:Dicarboxylic Acids; D007773:Lactates; D008293:Malates; D026901:Membrane Transport Proteins; D013386:Succinates; D014233:Tricarboxylic Acids; D019344:Lactic Acid; C030298:malic acid; D019802:Succinic Acid