The relationship of adenosine and inosine transport in Escherichia coli

Adenosine and inosine are rapidly taken up by suspensions of Escherichia coli by transport processes that can be differentiated from the slower subsequent formation of phosphorylated intermediates. The uptake mechanisms are saturable, are inhibited by heavy metal ions and energy poisons, and show a high temperature coefficient near 0°. Inosine efflux is also markedly temperature dependent and is inhibited by heavy metal ions. Efflux of inosine is increased by the influx of other nucleosides. Other nucleosides lower the rates of adenosine and inosine entry but free bases show little inhibition. Caffeine retards the rates of inosine influx and efflux but does not effect the adenosine uptake mechanism.

Transport can also be measured by the rate of deamination of adenosine by intact cells. Comparison of the similarities and differences for isotope uptake, release, and cellular deamination leads to the conclusion that adenosine and inosine are transported across the cell membrane by processes that are separate, but overlapping, and which have a facultative requirement for metabolic energy.