Expression of β3 containing additional β3¹¹⁷ substitutions in COS-1 cells. Transient expression studies in COS-1 cells were performed using either β3 mutants alone (A) or in combination with wild-type αIIb (B and C). In (A) and (B), the recombinant proteins were immunoprecipitated with SSA6 and in (C) with A2A9. The specific mutation introduced at β3¹¹⁷ is indicated for each lane. WT is the wild-type complex. Pro-αIIb corresponds to the single-chain αIIb precursor; αIIb-α corresponds to the αIIb heavy chain.