FIGURE 3.

Turnover and ADP sensitivity of phosphoenzyme. Phosphorylation was carried out with 5 μm [γ-³²P]ATP for 10 s on ice in the presence of 40 mm MOPS/Tris (pH 7.0), 80 mm KCl, 5 mm MgCl₂, 1 mm EGTA, 0.955 mm CaCl₂ (10 μm free Ca²⁺), and 2 μm calcium ionophore A23187. Dephosphorylation was followed by acid quenching at the indicated time intervals after a chase with 6.7 mm EGTA (•). For comparison, the wild-type (WT) data from the upper left panel are indicated in all panels by the dashed line. The ADP-insensitive E2P fraction of the phosphoenzyme was determined by the addition of 0.9 mm ADP 2 s prior to acid quenching (○).