Electrolytes in biological systems, incorporating Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954 electrolytesinbi00shan Year: 1955 DEAN B. COWIE AND RICHARD B. ROBERTS 7 the trichloroacetic acid soluble and insoluble fractions of the cell is also evident in figure 2. Glucose is required for this metabolic uptake of sulfate (10). Cells immersed in synthetic medium, complete with the exception of glucose, do not incorporate sulfur metabolically. Upon the addition of glucose,
Electrolytes in biological systems, incorporating Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954 electrolytesinbi00shan Year: 1955 DEAN B. COWIE AND RICHARD B. ROBERTS 7 the trichloroacetic acid soluble and insoluble fractions of the cell is also evident in figure 2. Glucose is required for this metabolic uptake of sulfate (10). Cells immersed in synthetic medium, complete with the exception of glucose, do not incorporate sulfur metabolically. Upon the addition of glucose, growth begins, and there is a direct correlation among growth, nitrogen content, and sulfate uptake. Except at extremely low concentrations of sulfate, the quantity of sulfur metabolically bound is independent of the concentration in the medium. QUANTITY OF NEW CELLS GROWN Fig. 2. Sulfate uptake during growth (£. coli). The upper curve shows the total radiosulfate uptake as a function of the quantity of new cells grown. The lower curve shows the radio- sulfur of the TCA soluble fraction as a function of growth. It is obvious from the preceding experiments that if the wash procedures were not carried out, large quantities of nonmetabolized sulfur passively held by these cells could constitute a potential source of error in the study of cell metabolism. Exchange and Wash Losses During Growth. Further comparison of the uptake of radiosulfate by resting and by growing cells may be made using wash-loss measurements. Cells grown in radiosulfate from a light inoculum were washed to remove water space sulfur and immersed in complete media containing various nonradioactive sulfur sources. It can be seen in table 5 that little of the labeled sulfur exchanged with the sulfur of the medium despite continuous cellular growth. The fact that no large losses of metabolically bound
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