Passive diffusion of nucleosides into Micrococcus sodonensis membrane vesicles.

Nucleoside entry into isolated membrane vesicles of Micrococcus sodonensis (luteus) was studied using 14C-labelled nucleosides: adenosine, inosine, cytidine, uridine, guanosine, and thymidine. All nucleosides were recovered unmetabolized from the vesicles except adenosine and cytidine which were partly deaminated by membrane-bound enzymes. Vesicle preparations actively transported proline but no energy source was found capable of supporting concentrative nucleoside uptake. The entry of nucleosides into M. sodonensis vesicles was not saturable, nor was there competition between the nucleosides studied for entry. It was concluded that nucleoside entry into M. sodonensis vesicles occurs by passive diffusion.