Mechanism of energy coupling for transport of deoxycytidine, uridine, uracil, adenine and hypoxanthine in Escherichia coli

Stimulatory effect of low ATP pools on transport of purine nucleosides in cells of Escherichia coli.

“…The residual nucleoside transport is probably due to incomplete starvation; i.e., the cells were deprived of ATP, but retained metabolites that could support energization of the membrane. The finding that the nucleoside transport also occurred in the presence of arsenate seems to exclude ATP as a necessary driving force, whereas the strong inhibitory effect of uncoupling agents on the transport is consistent with a proton motive force as the main energizer, as also suggested by the results of Roy-Burman et al (10) Although ATP is thus excluded as the immediate driving force for nucleoside transport, the results suggest another relationship between the cellular levels of ATP and the purine nucleoside-transporting part of the nupG system. Cells without a functional ATPase show an increased transport of purine nucleosides in the absence of glycolytic substrates compared to the isogenic wild-type cells (Fig.…”

“…The main purpose of the present work was to study the energization of the nupG system in mutants of E. coli containing only this transport system and, in addition, carrying a mutation in the Ca2+-and Mg2+-dependent ATPase (10). On the other hand, the results seem to assign a regulatory role to ATP (or a closely related compound) because depletion of ATP in cells has a specific stimulatory effect on the transport of purine nucleosides.…”