Unexpected additional mode of energization of amino-acid transport into Ehrlich cells.

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Abstract
Ehrlich cells treated with dinitrophenol and iodoacetate rapidly recovered their 30 s uptake of 2-(methylamino)-isobutyrate on treatment with 0.1 mM phenazine methosulfate + 20 mM sodium ascorbate before they began to recover from the severely depressed ATP levels and alkali-ion gradients. Addition of 10 mM pyruvate also restored uptake of methylaminoisobutyrate before the alkali-ion gradients rose. This restoration was prevented by rotenone, but rotenone did not handicap restoration by phenazine methosulfate/ascorbate. Na+-independent uptake of 2-aminonobornane-2-carboxylate by Ehrlich cells was affected the same way. Quinacrine almost completely suppressed uptake of methylaminoisobutyrate within the 30 s uptake test, even when ATP levels were sustained by pyruvate and alkali-ion gradients were not depressed. Ouabain prevented restoration of both Na+-dependent and Na+-independent amino-acid transport by phenazine methosulfate/ascorbate or pyruvate. Amino acid transport can be energized not only by known means, but also by reducing equivalents, which reach the plasma membrane in the form of NADH from the mitochondria when the source of energy is pyruvate. The distribution of methylaminoisobutyrate between plasma membrane vesicles and their supporting media was influenced in the predictable way by NADH, quinacrine and an uncoupling agent, proceeding on the assumption that more of the vesicles had the everted rather than the natural orientation.