engleski

The transport of pyrimidine bases in E.coli

The present work deals with experiments made to characterise transport of thymine and uracil in E.coli K12S grown in the glucose-mineral medium. Using a membrane filter method and 2-14C labelled bases, total uptake was determined by measuring radioactivity dissapearance from the medium, incorporation, pool formation and evolution of 14CO2. In glucose mineral medium, the majority of 2-14C uracil (0.5 micromolar) was taken up and retained by the cells, while a small portion was degraded to 14CO2. 2-14C thymine under the same conditions, did not enter the cells. With the bacteria preincubated in the medium without ammonium ions, both bases dissapeared from the medium at approximately the same initial rate. The fact that all radioactivity from thymine and a majority from uracil was recovered in 14CO2, indicates that in the absence of ammonium ions transport system for thymine was induced. This was supported by the finding that the presence of chloramphenicol decreased the total uptake of thymine but not that of uracil. In this case however, the majority of radioactivity from uracil remained undegraded within the cells. N-Ethylmaleimide, and to a lesser extent KCN, inhibited the total uptake of both bases, while sodium azide interferred only with incorporation and pool formation of 2-14C uracil and its derivatives. The results suggest a regulatory effect of ammonium ions in the active transport of pyrimidine bases.

Escherichia coli; pyrimidine bases

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