Sodium and Potassium Requirements for Active Transport of Glutamate by Escherichia coli K-12

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Abstract
Active transport of glutamate by Escherichia coli K-12 requires both Na + and K + ions. Increasing the concentration of Na + in the medium results in a decrease in the K m of the uptake system for glutamate; the capacity is not affected. Glutamate uptake by untreated cells is not stimulated by K + . K + -depleted cells show a greatly reduced capacity for glutamate uptake. Preincubation of such cells in the presence of K + fully restores their capacity for glutamate uptake when Na + ions are also present in the uptake medium. Addition of either K + or Na + alone restores glutamate uptake to only about 20% of its maximum capacity in the presence of both cations. Changes in K + concentration affect the capacity for glutamate uptake but have no effect on the K m of the glutamate transport system. Ouabain does not inhibit the (Na + -K + )-stimulated glutamate uptake by intact cells or spheroplasts of E. coli K-12.

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