FIG. 4.

Intracellular pH optima of glutamate and arginine decarboxylases correlate to the internal pH of acid-stressed cells. EK227 cells were grown to stationary phase in LBG. Conversions of glutamate and arginine to GABA and agmatine, respectively, were carried out essentially as described in the legend for Fig. 3. Cells, either intact or Triton X solubilized, were resuspended at different pH values, and radiolabeled substrate was added.