FIG. 1.

pH dependence of the Ca-loaded (open symbols) and Ca-free (closed symbols) CEP activity at 10°C (——). The results obtained with two different cell suspensions with equal activities at pH 6.0 are shown. For comparison activities measured at 25°C are also shown (–––); the values of these activities were positioned on the vertical scale by normalizing them to an activity of the Ca-loaded CEP at pH 6.2 equal to that at 10°C. For the Ca-free CEP at 25°C, only activities in the pH range of 5.8 to 7.0 are shown in order to illustrate the effect removal of Ca²⁺ has at this temperature. The discontinuities in the curves (with or without a change in the symbol) represent the changes in the buffer system used. For further details, see Materials and Methods.