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

Ehrlich cells treated with dinitrophenol and iodoacetate rapidly recover their 30-sec uptake of 2-(methyl-amino)-isobutyrate on treatment with 0.1 mM phenazine methosulfate + 20 mM sodium ascorbate before they begin to recover from the severely depressed ATP levels and alkali-ion gradients. Addition of 10 mM pyruvate also restores uptake of methylaminoisobutyrate before the alkali-ion gradients rise. This restoration is prevented by rotenone, but rotenone does not handicap restoration by phenazine methosulfate/ascorbate. Na+-independent uptake of 2-aminonorbornane-2-carboxylate by Ehrlich cells is affected the same way. Quinacrine almost completely suppresses uptake of methylaminoisobutyrate within the 30-sec uptake test, even when ATP levels are sustained by pyruvate and alkali-ion gradients are not depressed. Ouabain prevents restoration of both Na+-dependent and Na+-independent amino-acid transport by phenazine methosulfate/ascorbate or pyruvate. We interpret these results to indicate that amino-acid transport can be energized not only by known means, but also by reducing equivalents, which presumably reach the plasma membrane in the form of NADH from the mitochondria when the source of energy is pyruvate. In support of this hypothesis, 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.