FIGURE 4.

Be²⁺ dependence of the rate of EP inhibition by BeF_x in 0.01 mm Ca²⁺. A, microsomes expressing the wild type or mutant 4Gi-46/47 were incubated for various periods in 0.01 mm Ca²⁺ and 1 mm KF with various concentrations of BeSO₄ and otherwise as in Fig. 3, A and C, for BeF_x-treatment. The samples were then diluted 10-fold and phosphorylated with 10 μm [γ-³²P]ATP, and the amount of EP formed was determined, as in Fig. 3, A and C. Solid lines show the least squares fit to a single exponential. In B, the rate constants obtained in A were plotted versus the concentration of Be²⁺ added. The linear fit to the data gave a slope of 0.123 min^−1μm−1.