The interaction between an isoform of CTX and FXa, as measured by SPR. The anti-CA monoclonal antibody mAb A-73.13  was covalently attached to the chip . CTX (the CA2-CBc complex) was then captured via this mAb before injection of FXa (25 μg/ml). FXa bound to CTX, as seen in the rise of the resonance signal, showing that the CTX-FXa complex remained attached to the anti-CA mAb. After injection of a specific anti-CB MAb (B-32.13, 10 μg/ml), the signal increased further, confirming the presence of CB in the ternary CA-CB-FXa complex.