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SUMMARY: Thermus thermophilus B is one of the many Thermus strains able to utilize glutamate as a sole source of carbon. Sodium is an obligate requirement for glutamate transport by washed whole cells, but the affinity for sodium (K m = 23 mM) is low. At pH 7.6, uptake of glutamate is rapid in 50 mM-sodium at 65 °C and obeys saturation kinetics with an apparent K m of 0.23 μ;M-glutamate and a V max of 12 nmol glutamate min-1 (mg protein)-1. The transport system is insensitive to osmotic shock and is specific for glutamate, with both the L- and D-isomers being transported. Uptake is very sensitive to inhibitors that collapse the membrane potential (Δψ) or the chemical gradient of sodium ions (ΔpNa), but a transmembrane pH gradient (ΔpH) plays no role in the transport of glutamate. These results are therefore consistent with a membrane sodium/glutamate symport system.
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