Mechanism of Energy Coupling For Transport of d-Ribose in Escherichia coli

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In Escherichia coli ML 308-225, d-ribose is transported into the cell by a constitutive active transport system of high activity. The activity of this transport system is severely reduced in cells subjected to osmotic shock, and the system is not present in membrane vesicles. The mechanism by which metabolic energy is coupled to transport of ribose was investigated. Substrates which generate adenosine 5′-triphosphate primarily through oxidative phosphorylation are poor energy sources for ribose uptake in DL-54, a mutant of ML 308-225 which lacks activity for the membrane-bound Ca2+, Mg2+-dependent adenosine triphosphatase required for oxidative phosphorylation. Arsenate severely inhibits ribose uptake, whereas, under the same conditions, uptake of l-proline is relatively insensitive to arsenate. Anaerobiosis does not significantly inhibit ribose uptake in ML 308-225 or DL-54 when glucose is the energy source. A significant amount of ribose uptake is resistant to uncouplers of oxidative phosphorylation such as 2,4-dinitrophenol. These results indicate that the phosphate bond energy of adenosine 5′-triphosphate, rather than an energized membrane state, couples energy to ribose transport in ML 308-225.

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