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Transport of lactic acid in Kluyveromyces marxianus : Evidence for a monocarboxylate uniport
Author(s) -
Fonseca A.,
SpencerMartins I.,
Van Uden N.
Publication year - 1991
Publication title -
yeast
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.923
H-Index - 102
eISSN - 1097-0061
pISSN - 0749-503X
DOI - 10.1002/yea.320070803
Subject(s) - lactic acid , antiporter , biochemistry , symporter , bicarbonate , biology , chemistry , membrane , bacteria , organic chemistry , genetics , transporter , gene
Lactic acid‐grown cells of a strain of Kluyveromyces marxianus transported D ‐and L ‐lactic acid by a saturable mechanism that was partially inducible and subject to glucose repression, with the following kinetic parameters at pH 5·4: V max = 1·00 (±0·13) mmol h −1 per g dry weight and K s = 0·42 (±0·08) m M . Lactic acid transport was competitively inhibited by pyruvic, glycolic, acetic and bromoacetic acids. The latter, a non‐metabolizable analogue, was transiently accumulated, the extent depending on the extracellular pH. The pH dependence of the K s values for undissociated lactic acid and for the lactate anion indicated that the latter was the transported species. Lactate uptake was not accompanied by the simulatate uptake of protons, potassium ions or sodium ions excluding symport mechanisms. Initial lactic acid uptake led to transient membrane hyperpolarization as measured with a fluorescent dye excluding also an electroneutral anion antiport mechanism. It was concluded that lactate anions use a monocarboxylate uniport and that the counter anion, possibly bicarbonate, uses a separate channel, the coupling being electrical and loose.