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, I1(PP2A) and I2(PP2A). Immunoprecipitation assay using Xenopus egg extract showed that I1(PP2A) bound B ''/PR48, and I2(PP2A) bound B56 gamma and B ''/PR48 among four B subunits analyzed. Thus I1(PP2A) and I2(PP2A) 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. (C) 2015 Elsevier Inc. All rights reserved.