Differential transport properties of D-leucine and L-leucine in the archaeon, Halobacterium salinarum.
The transport of D-leucine was compared with that of L-leucine in Halobacterium salinarum. When a high-outside/low-inside Na+ gradient was imposed, D-leucine as well as L-leucine accumulated in envelope vesicles, supporting the hypothesis that D-leucine is transported via a symport system along with Na+. Kinetic analyses, including inhibition experiments, indicated that both enantiomers are transported via a common carrier. However, a Hill plot indicated a single binding site for Na+ during L-leucine transport, but dual binding sites for Na+ during D-leucine transport. Furthermore, D-leucine transport was dependent on electrical membrane potential, suggesting that a transporter bound with D-leucine is positively charged. L-leucine transport was slightly, if at all, dependent on membrane potential, suggesting that a transporter bound with L-leucine is electrically neutral. These results indicate that the leucine carrier in Halobacterium salinarum translocates two moles of Na+ per mole of D-leucine, and one mole of Na+ per mole of L-leucine.
Tanaka
M
M
Department of Biology, Faculty of Science, Nagoya University, Japan. tanaka@nagoya.riken.go.jp
Mukohata
Y
Y
Yuasa
S
S
D001692:Biological Transport; D019617:Halobacterium salinarum / Q000254:growth & development / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008564:Membrane Potentials; D012964:Sodium / Q000378:metabolism; D013237:Stereoisomerism
D012964:Sodium; D007930:Leucine