Potassium Transport and the Relationship Between Intracellular Potassium Concentration and Amino Acid Uptake by Cells of a Marine Pseudomonad

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RESUMO

Transport of K+ by K+-depleted cells of marine pseudomonad B-16 (ATCC 19855) exhibited saturation kinetics. Rb+ inhibited both K+ transport and the K+-dependent transport of α-aminoisobutyric acid (AIB) into K+-depleted cells of the organism in proportion to the concentration of Rb+ in the suspending medium. Inhibition of the K+-dependent uptake of AIB into K+-depleted cells by Rb+ could be overcome by increasing the concentration of K+ in the medium. When AIB and K+ were added simultaneously to a suspension of K+-depleted cells, the uptake of K+ occurred immediately and rapidly, whereas the accumulation of AIB occurred only after a lag. The initial uptake rate of AIB was directly proportional to the intracellular K+ concentration. The intracellular concentration of K+ and AIB at their steady-state levels increased to a maximum as the Na+ concentration in the suspending medium was increased. At Na+ concentrations between 0.2 and 0.3 M, the molar ratio of K+ to AIB at their intracellular steady-state concentrations was constant at 1.6. At external Na+ concentrations less than 0.2 M, the cells maintained a relatively higher K+ intracellular steady-state level than AIB.

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