1. Terminate kinase reactions by adding equal volume of ice-cold 10% trichloroacetic acid (TCA) to each reaction.

2. Label 2.1 cm Whatman P81 phosphocellulose filter with a 2H pencil.

3. Spot an aliquot of the reaction/TCA mix onto the P81 phosphocellulose filter.

4. Wash the P81 filter three times with 500 ml cold 0.5% phosphoric acid (5-10 minutes per wash).

5. Rinse briefly in ethanol or acetone and air-dry on paper towels.

6. Transfer P81 filter into scintillation vials.

7. Add scintillation fluid and count.