Energetics of alanine, lysine, and proline transport in cytoplasmic membranes of the polyphosphate-accumulating Acinetobacter johnsonii strain 210A.
Amino acid transport in right-side-out membrane vesicles of Acinetobacter johnsonii 210A was studied. L-Alanine, L-lysine, and L-proline were actively transported when a proton motive force of -76 mV was generated by the oxidation of glucose via the membrane-bound glucose dehydrogenase. Kinetic analysis of amino acid uptake at concentrations of up to 80 microM revealed the presence of a single transport system for each of these amino acids with a Kt of less than 4 microM. The mode of energy coupling to solute uptake was analyzed by imposition of artificial ion diffusion gradients. The uptake of alanine and lysine was driven by a membrane potential and a transmembrane pH gradient. In contrast, the uptake of proline was driven by a membrane potential and a transmembrane chemical gradient of sodium ions. The mechanistic stoichiometry for the solute and the coupling ion was close to unity for all three amino acids. The Na+ dependence of the proline carrier was studied in greater detail. Membrane potential-driven uptake of proline was stimulated by Na+, with a half-maximal Na+ concentration of 26 microM. At Na+ concentrations above 250 microM, proline uptake was strongly inhibited. Generation of a sodium motive force and maintenance of a low internal Na+ concentration are most likely mediated by a sodium/proton antiporter, the presence of which was suggested by the Na(+)-dependent alkalinization of the intravesicular pH in inside-out membrane vesicles. The results show that both H+ and Na+ can function as coupling ions in amino acid transport in Acinetobacter spp.
Van Veen
H W
HW
Department of Microbiology, Agricultural University Wageningen, The Netherlands.
Abee
T
T
Kleefsman
A W
AW
Melgers
B
B
Kortstee
G J
GJ
Konings
W N
WN
Zehnder
A J
AJ
D000150:Acinetobacter / Q000378:metabolism*; D000409:Alanine / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D042843:Glucose 1-Dehydrogenase; D005948:Glucose Dehydrogenases / Q000378:metabolism; D007700:Kinetics; D008239:Lysine / Q000378:metabolism*; D008564:Membrane Potentials; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011122:Polyphosphates / Q000378:metabolism; D011392:Proline / Q000378:metabolism*; D011522:Protons; D012964:Sodium / Q000494:pharmacology
D002352:Carrier Proteins; D011122:Polyphosphates; D011522:Protons; D011392:Proline; D012964:Sodium; D005948:Glucose Dehydrogenases; D042843:Glucose 1-Dehydrogenase; D005947:Glucose; D008239:Lysine; D000409:Alanine