SUMMARY: The relationship of the pH value of the suspension medium to inorganic phosphate accumulation by , strain W, in the presence and absence of 2:4-dinitrophenol was studied. Investigations were conducted to ascertain whether variations of the conditions of culture influenced phosphate accumulation. The pH value of the suspension medium had an influence on the amount of radio-phosphate accumulation. The pH optimum, under the conditions used, was 6.5. The pH value of the culture medium, in the range tested, had little or no influence on the pH optimum observed in the suspensions, although differences in total phosphate accumulation were noted. Approximately 70% of the orthophosphate accumulated by the organisms was in the form of inorganic phosphate, which leads to the postulate of an active transport mechanism for phosphate accumulation in Tetrahymena. 2:4-Dinitrophenol was most effective in lowering radiophosphate accumulation in an acidic medium, and became less effective with increasing alkalinity. The results can be explained on the basis of the penetration of only the undissociated molecule into the organisms. It is suggested that 2:4-dinitrophenol interferes with the transport mechanism involved in phosphate entry.


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