OBSERVATIONS ON THE AMINO ACID POOL AND CELLULAR LEAKAGE IN INTACT CELLS OF RHIZOBIUM MELILOTI

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Abstract
Cells of Rhizobium meliloti contained an intracellular pool of amino acids. The passage of C14-histidine or C14-glutamate into this pool apparently occurred against a concentration gradient and was energy dependent, being inhibited by azide and dinitrophenol. An internal bound form of C14, containing a number of radioactive amino acids, was synthesized at the expense of radioactive pool components. This bound C14consisted predominantly of several proteins whose syntheses were inhibited by chloramphenicol. Added histidine was not incorporated directly into this protein since the protein histidine was nonradioactive. When C14-labelled cells were suspended in glucose-containing basal medium there was an efflux of pool amino acids into the extracellular environment. This leakage presumably was the result of simple diffusion since it was energy independent, occurred with the concentration gradient, and was appreciable at 5 °C. Rapid leakage occurred at 30 °C in the presence and absence of dinitrophenol for an initial period of 6 hours, after which time growth occurred in the absence of this inhibitor. During growth leakage ceased, and a considerable quantity of material passed back into the cells and was incorporated into a bound form. In the presence of dinitrophenol no growth occurred, and the outflow continued after the 6th hour, but at a much reduced rate. X irradiation increased the efflux of pool constituents, but the reason for this is conjectural.