文摘
The amino acid sequences of two tryptic peptides derived frompurified preparations of I1PP2Aindicated that this potent heat-stable protein inhibitor of proteinphosphatase 2A (PP2A) may be equivalentto putative histocompatibility leukocyte antigens class II-associatedprotein I (PHAP-I). Experimentsusing purified preparations of recombinant human PHAP-I confirmed thatthis protein inhibited PP2A.Half-maximal inhibition of the phosphatase occurred at about 4 nMPHAP-I, similar to the half-maximalinhibition obtained with purified preparations of bovine kidneyI1PP2A. In addition, PHAP-I did notaffectthe activities of protein phosphatase 1, 2B, and 2C in a manneranalogous to that of I1PP2A. Together,theresults establish the identity of I1PP2A on afirm basis.