Effect of Gln747 → Ala substitution on _IIbβ₃ expression and PAC-1 binding to wild-type and mutant _IIbβ₃ activated with PT25-2 MoAb. The _IIb cDNA containing the Gln747 → Ala substitution was cotransfected with wild-type β₃ cDNA into 293 cells. The transfected cells were incubated with AP2 or PT25-2 for 30 minutes on ice and washed once, and bound antibodies were detected by FITC-conjugated goat F(ab′)₂ antimouse IgG. For PAC-1 binding, PT25-2–treated or FK633-treated 293 cells were incubated with FITC-labeled PAC-1 for 30 minutes on ice. Results are expressed as histograms of cell number (linear scale) on the ordinate versus fluorescence intensity (log scale) on the abscissa.