Energization of Active Transport by Escherichia coli

Abstract An activated membrane state necessary for the active transport of certain amino acids, carbohydrates, and cations by Escherichia coli can be generated by either oxidative energy or phosphate bond energy. Membrane fragment vesicles from E. coli couple oxidative but not phosphate bond energy to the transport of proline. The vesicles show an O2-dependent transport yet lack measureable capacity for oxidative phosphorylation. Such transport is arsenate-resistant, consistent with the transport being independent of oxidative phosphorylation. Although vesicles possess ATPase activity, added ATP does not stimulate proline transport. With intact E. coli cells, incubation with high arsenate and low phosphate drastically lowers intracellular ATP and P-enolpyruvate levels in the presence or the absence of O2. Aerobic proline transport is uninhibited, but in contrast, anaerobic transport is sharply reduced. These results show that intact cells can use energy either from oxidations or from phosphorylations to drive active proline transport. Similarly, active accumulation of leucine, β-methylthiogalactoside, Rb+ (as a K+ analogue), and α-methylglucoside occurs aerobically in the presence of high arsenate. Uncouplers of oxidative phosphorylation block the use of energy for transport both from oxidations and from ATP, suggesting that a similar or identical energy-conserving membrane state is formed from either energy source. Transport of α-methyl glucoside by intact E. coli is only partially inhibited by the high arsenate-low phosphate incubation, and further, part of the transported sugar still appears intracellularly in the phosphorylated form. The glucose-6-P level remains high in presence of arsenate and this or other intracellular phosphate compounds may be involved in phosphorylation of the transported sugar by an unknown mechanism. Low concentrations of iodoacetate nearly completely block the α-methylglucoside transport with but little effect on the O2-driven proline transport.