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

Cells of Escherichia coli contain two nucleoside-transport systems. Energy-starved cells of a strain containing only one of these systems and, in addition, carrying a mutation in the Ca2+- and Mg2+-dependent ATPase (ATP phosphohydrolase 3.6.1.3) are still able to transport nucleosides. The rate is only slightly lower than the rate measured in unstarved cells. Freshly harvested uncA cells transport purine nucleosides at a higher rate than cells from the isogenic strain containing a functional ATPase. If cells from the latter strain are treated with arsenate, transport rates increase to the same levels as found in uncA cells. The presence of an uncA mutation has no effect on the transport rates for cytidine, deoxycytidine, and uridine, nor has arsenate treatment. These findings indicate that ATP is not required as energy donor for nucleoside transport. The enhanced transport rate for purine nucleosides after treatment with arsenate seems to suggest a regulatory relationship between the transport of these nucleosides and the cellular levels of ATP or a closely related metabolite.