Quantitative VWF binding to platelet integrin α_IIbβ_III. The α_IIbβ_III head group has been crystallized by Zhu et al⁵¹  and is constitutively active. AP3 was used as a capture antibody for α_IIbβ_III. Heat-defibrinated standard or test plasma was added and washed with the bound VWF detected with a biotinylated monoclonal antibody to VWF. Binding was inhibited by 7E3. VWF binding to α_IIbβ_III was high-molecular-weight multimer dependent, similar to VWF binding to GPIb and collagen.