To determine the activity of all human Cdc25 phosphatases, two different methods are described. For assaying phosphatase activities of recombinant Cdc25 proteins produced inEscherichia colior insect cells, a fluorimetric assay using fluorescein diphosphate (FDP) as a substrate is recommended. To analyze endogenous Cdc25 phosphatase activities of immuno-precipitates from total cellular extracts, the physiological substrate Cdk1/cyclin B1 is most sensitive.
