Postirradiation release of adenosine triphosphate from Escherichia coli[formula omitted

Abstract

The effect of x-rays on adenosine triphosphate (ATP) metabolism of Escherichia coli B r has been investigated. ATP was assayed for by use of the firefly luminescent system. The following results were obtained: 1. 1. Exposure to 60,000 r. did not alter the initial ATP content of the cells. 2. 2. The irradiated cells, when incubated at 37 °C. in a nutrient broth containing glucose, appeared to be capable of forming ATP at a rate approximately equal to that of the control cells. 3. 3. Irradiated cells, separated from the incubating medium, showed a decreasing ATP content with increasing incubation time. An analysis of the supernatant from these cultures revealed an increasing concentration of ATP with increasing time of incubation. No such release of ATP was noted from the nonirradiated cells. 4. 4. The presence or absence of metabolites in the incubating medium markedly influenced the degree of ATP loss into the medium. The loss of ATP was noted only under those conditions in which a turnover of ATP might be expected. 5. 5. The rate of release of ATP by the irradiated cells incubated in nutrient broth plus glucose was decreased if the temperature was lowered below 37 °C. Irradiated cells incubated in phosphate buffer plus glucose exhibited a lag in ATP loss, the duration of this lag increasing as the temperature was decreased below 37 °C. 6. 6. The amount of ATP lost by irradiated cells during 90 min. incubation at 37 °C. was found to increase with increasing x-ray dose. 7. 7. On the basis of evidence obtained by turbidity measurements, microscopic observations, and cell counts, the possibility that gross lysis of the irradiated cells is responsible for the release of ATP into the medium is eliminated. However, the evidence does not eliminate the possibility of a subtle form of lysis or structural change, rather than a true permeability change in the cell membrane, being the cause of the ATP leakage.