Transient expression of IIb^P145 mutations in COS-1 cells.

(A) Wild-type αIIb (WT) and the indicated αIIb^P145mutants were expressed in COS-1. An equal number of cells for each transfection were then labeled with ³⁵S-methionine, and αIIb was immunoprecipitated with the use of the αIIb-specific monoclonal antibody B1B5. P/S refers to a proline and serine swap at amino acid residues 144 and 145. (B) COS-1 cells co-transfected with either wild-type αIIb or the indicated αIIb^P145 mutants and β3. After the cells were labeled with ³⁵S-methionine, αIIbβ3 was immunoprecipitated with the β3-specific monoclonal antibody SSA6. The identity of β3 was confirmed by immunoprecipitation of control platelets (Plt) surface-labeled with¹²⁵I. (C) Immunoprecipitation of αIIbβ3 with the use of SSA6 from cells, cotransfected with either wild-type αIIb or the indicated αIIb^P145 mutants and β3, which were surface-labeled with ¹²⁵I. The data shown are representative of 3 separate experiments.