FIGURE 5.

Ca²⁺ dependence of accumulation of ADP-insensitive EP in mutants for Tyr¹²²-hydrophobic cluster. Microsomes expressing each of the seven Y122-HC mutants (indicated in the figure) were phosphorylated with [γ-³²P]ATP at various concentrations of Ca²⁺ and pH 7.3, otherwise as described in Fig. 2. Solid lines show the least squares fit to the Hill equation. The fitting parameters, including the apparent Ca²⁺ affinity and the Hill coefficient, thus obtained are listed in Table 1.