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Specific Electron Donor-Energized Transport of -Aminoisobutyric Acid and K⁺ into Intact Cells of a Marine Pseudomonad

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

ABSTRACT

The transport of -aminoisobutyric acid and K⁺ into K⁺-depleted cells of a marine pseudomonad (ATCC 19855) was stimulated strongly by ethanol, reduced nicotinamide adenine dinucleotide (NADH), and ascorbate-reduced N, N, N', N'-tetramethyl-p-phenylenediamine. In the presence of the quinone inhibitor 2-heptyl-4-hydroxyquinoline-N-oxide, only ascorbate-reduced N, N, N', N'-tetramethyl-p-phenylenediamine was active. Primary and secondary, but not tertiary, alcohols from ethanol to n-amyl alcohol stimulated both -aminoisobutyric acid and K⁺ transport and were oxidized by the cells. Malate and succinate, which were oxidized rapidly by the cells, had little or no capacity to energize the transport of -aminoisobutyric acid into K⁺-depleted cells but were partially effective in promoting K⁺ uptake. Ethanol stimulated the transport of -aminoisobutyric acid into K⁺-preloaded cells. The transport of both -aminoisobutyric acid and K⁺ was inhibited 20% by iodoacetate, 85% by N-ethylmaleimide, and 90 to 100% by both NaCN and p-chloromercuribenzoate. The addition of Na₃Fe(CN)₆ permitted the ethanol-induced transport of -aminoisobutyric acid into K⁺-preloaded cells in the presence of NaCN, but little or no uptake of -aminoisobutyric acid or of K⁺ into K⁺-depleted cells under the same conditions. The transport of -aminoisobutyric acid into K⁺-depleted cells required both K⁺ and an electron donor. The oxidation of NADH and ethanol by K⁺-depleted cells was stimulated strongly by K⁺. Parallels between these studies and those with membrane vesicles show that results with membrane vesicles of the marine pseudomonad have physiological significance for the intact cells. The results support the conclusion that the energy for the active transport of both -aminoisobutyric acid and K⁺ into cells of this organism is provided by electron flow through a region of the respiratory chain lying between cytochrome c and O₂.

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