FIGURE 2.

Dependence of the 2BITC fluorescence on pH in Ca-ATPase-containing SR vesicles. Equilibrium titration experiments were started at high pH and performed by addition of appropriate aliquots of HCl. The electrolyte contained besides 20 mM Bis-Tris, 0.2 mM EDTA, 9 μg/ml SR Ca-ATPase, 200 nM 2BITC 10 mM NaCl (•), 10 mM KCl (□), or 100 mM KCl (Δ). The respective lines are regression lines calculated through the data point in the pH range 5.5–7.5. (T = 21°C).