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

^a The Department of Microbiology, Macdonald Campus, McGill University and Marine Sciences Centre, McGill University Montreal, Quebec, Canada

ABSTRACT

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 -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.

¹ Present address: Biochemistry Division, Dairy Research Institute, Palmerston North, New Zealand.