Chromatographic resolution of soluble and particulate protein phosphatases from Dictyostelium discoideum

We have examined protein phosphatase activities that are present during the cellular differentiation of Dictyostelium. Utilizing differential centrifugation, ion exchange, gel filtration, and concanavalin A affinity chromatography we found a number of distinct protein phosphatase activities. Three peaks of soluble Kemptide phosphatase activity and a very broad and heterogeneous soluble histone phosphatase activity were resolved by anion exchange chromatography. Histone phosphatase was associated with the particulate fraction, while Kemptide phosphatase was not. The protein phosphatase activities were able to dephosphorylate sites that had been phosphorylated by the cyclic AMP-dependent protein kinase. Therefore it is possible that their function in vivo may be to oppose the action of the cAMP-dependent protein kinase. In addition several paranitrophenyl phosphate phosphatase activities are shown to be largely separable from the protein phosphatases. An apparent heat-stable inhibitor of histone phosphatase is shown to be artifactual in that instead of interacting with the enzyme it acts by complexing with histone.