Fig. 8. Dephosphorylation of p130 by RPTPß. (A) MAGI-3 immunocomplexes from vanadate-treated SF763T cells were incubated with GST or GST-fusion proteins containing the cytoplasmic domain of RPTPß (ßD12), a catalytic inactive mutant (ßD12DA), the first phosphatase domain (ßD1) or a mutant form lacking the C-terminus (ßD12dCT) as indicated. The reaction was terminated by the addition of SDS gel loading buffer, and the samples were immunoblotted with anti-phosphotyrosine (upper panel) or anti-MAGI-3 (lower panel) antibodies. Treatment of the immunocomplexes with alkaline phosphatase (AP) was used as a positive control. (B) Coommassie blue staining of the RPTPß constructs used in panel A. (C) Phosphatase activity. The indicated RPTPß GST-fusion proteins were incubated with p-nitrophenilphosphate as described in experimental procedures, and the absorbance of the reaction product was measured at 450 nm.