Effect of STO-609 on the activities of CaMKK isoforms with Mg-GTP. A. Recombinant CaMKKα (·) or recombinant CaMKKβ (○) was incubated with GST-CaMKIα (1-293, K49E, 0.5 mg/ml) at 30°C for 4 min in the presence of 50 μM [γ-32P]GTP and 2 mM CaCl2/4 μM CaM with various concentrations of STO-609 (0 – 10 μg/ml) as described in "Methods." Activities are expressed as a percentage of the value in the absence of STO-609. Results represent mean and S.E. of three experiments. B. Protein kinase activities of purified recombinant CaMKKα (B, left panel) and β (B , right panel) were measured with various concentrations (100 – 400 μM) of [γ-32P]GTP in either the absence (○) or presence (·) of 0.1 μg/ml STO-609 for CaMKKα and in either the absence (○) or presence (·) of 0.01 μg/ml STO-609 for CaMKKβ. The results represent duplicate experiments and are presented as double reciprocal plots (Lineweaver-Burk).