MECHANISM OF UPTAKE OF PURINES BY PSEUDOMONAS AERUGINOSA

During growth inhibition, 8-azaxanthine is incorporated into the ribonucleic acid of Pseudomonas aeruginosa. The azaxanthine-resistant strain, which emerges after about 10-hr exposure, doesnot incorporate the antimetabolite any more. Although xanthine or hypoxanthine does not stimulate growth, they undergo incorporation into the ribonucleic acid. The experiments with labeled purines indicate that a common mechanism serves for the uptake of xanthine, 6-thioxanthine, and 8-azaxanthine from the external medium into the protoplasm, and that this mechanism has changed in the azaxanthine-resistant strain. Incorporation of hypoxanthine and 6-mercaptopurine into the ribonucleic acidproceeds along a different path, which is not altered by 8-azaxanthine. In each of the two different mechanisms, only purines of related structure compete with each other. 3-Methylxanthine is not absorbed by the Pseudomonas but suppresses the uptake of xanthine or 6-thioxanthine; suppression is more effective in the azaxanthine-resistant strain than in the wild type. Therefore, competition most likely takes place on the cell surface. © 1969, American Chemical Society. All rights reserved.