Inhibitor-1 and -2 of PP2A have preference between PP2A complexes

Protein phosphatase 2A (PP2A) forms tens of kinds of complexes with different substrate specificity and functions by using various regulatory B subunits. But how these complexes' activities are regulated separately is not well understood. Here we showed unequal enzyme inhibition of each form by two proteinous PP2A inhibitors, I1PP2A and I2PP2A. Immunoprecipitation assay using Xenopus egg extract showed that I1PP2A bound B″/PR48, and I2PP2A bound B56γ and B″/PR48 among four B subunits analyzed. Thus I1PP2A and I2PP2A seem to have B-subunit specificity. These results support the hypothesis that PP2A complexes containing common catalytic subunit are individually regulated for their separate functions in vivo.