On the 6-phosphofructo-1-kinase phosphatase activity of protein phosphatase 2C and its dimeric nature

A recently described 6-phosphofructo-1-kinase phosphatase (PFK-phosphatase) shared several properties with protein phosphatase 2C, but exhibited differences with respect to molecular mass and substrate specificity. Chromatography on histone-Sepharose, gel filtration experiments on Sephacryl S-200 and Sephadex G-100 as well as sucrose density gradient centrifugation show that both enzyme preparations behave identically under all experimental conditions used. The low activity of PFK-phosphatase phosphorylated histone H2B had resulted from an inhibition of the enzyme by high concentrations of this substrate. The apparent molecular mass of protein phosphatase 2C as calculated from Sephacryl chromatography and sedimentation analysis is about 90 kDa, the molecular mass obtained by SDS gel electrophoresis about 45 kDa. The native enzyme therefore seems to be a dimer consisting probably of 2 identical subunits. Accordingly, the previously described PFK-phosphatase is protein phosphatase 2C.