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Applied and Environmental Microbiology, September 2001, p. 4144-4151, Vol. 67, No. 9
UMR Sciences pour
l'Oenologie-Laboratoire de Microbiologie et Technologie des
Fermentations, Institut National de la Recherche Agronomique,
F-34060 Montpellier Cedex 1, France
Received 5 March 2001/Accepted 19 June 2001
In Saccharomyces cerevisiae, L-malic acid
transport is not carrier mediated and is limited to slow,
simple diffusion of the undissociated acid. Expression in S. cerevisiae of the MAE1 gene, encoding
Schizosaccharomyces pombe malate permease, markedly
increased L-malic acid uptake in this yeast. In this
strain, at pH 3.5 (encountered in industrial processes),
L-malic acid uptake involves Mae1p-mediated transport of
the monoanionic form of the acid (apparent kinetic parameters:
Vmax = 8.7 nmol/mg/min;
Km = 1.6 mM) and some simple diffusion of the
undissociated L-malic acid (Kd = 0.057 min
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.9.4144-4151.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of Schizosaccharomyces pombe Malate
Permease by Expression in Saccharomyces
cerevisiae
1). As total L-malic acid transport
involved only low levels of diffusion, the Mae1p permease was further
characterized in the recombinant strain. L-Malic acid
transport was reversible and accumulative and depended on both the
transmembrane gradient of the monoanionic acid form and the
pH
component of the proton motive force. Dicarboxylic acids with stearic
occupation closely related to L-malic acid, such as maleic,
oxaloacetic, malonic, succinic and fumaric acids, inhibited
L-malic acid uptake, suggesting that these compounds use
the same carrier. We found that increasing external pH directly
inhibited malate uptake, resulting in a lower initial rate of uptake
and a lower level of substrate accumulation. In S. pombe, proton movements, as shown by internal acidification, accompanied malate uptake, consistent with the proton/dicarboxylate mechanism previously proposed. Surprisingly, no proton fluxes were
observed during Mae1p-mediated L-malic acid import in
S. cerevisiae, and intracellular pH remained constant.
This suggests that, in S. cerevisiae, either there is
a proton counterflow or the Mae1p permease functions differently from a
proton/dicarboxylate symport.
*
Corresponding author. Mailing address: UMR Sciences
pour l'
nologie Laboratoire de Microbiologie et Technologie des
Fermentations, INRA, 2 place Viala, F-34060 Montpellier Cedex 1, France. Phone:(33) 4 99 61 23 36.Fax: (33) 4 99 61 28 57. E-mail:
camarasa{at}ensam.inra.fr.
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