Figure 5. Binding of β₂GPI to ionomycin-activated blood platelets at low ionic strength.

(A) Binding of β₂GPI as a function of platelet concentration. Platelets were incubated with 200 nM β₂GPI for 15 min in isotonic Hepes buffer containing 20 mM NaCl. The incubation mixture was centrifuged and the concentration of free β₂GPI in samples from the supernatant was determined by ellipsometry. Shown is the concentration of bound β₂GPI as a function of the platelet concentration. (B) Binding of β₂GPI as a function of the concentration of β₂GPI. Platelets (6×10⁸ platelets·ml⁻¹) were incubated with various concentrations of β₂GPI in isotonic Hepes buffer containing 20 mM NaCl. After 15 min, the incubation mixture was centrifuged and the concentration of free β₂GPI in samples from the supernatant was determined by ellipsometry. Shown is the concentration of bound β₂GPI as function of the added β₂GPI concentration. The solid line represents the best fit of eqn (1) to these data.