Effect of mAb AP3 on binding of DDAb11 and DDAb16 to construct 1. The quinine-dependent reaction of DDAb11 (left) but not that of DDAb16 (right) with construct 1 (srGPIIIa) is blocked by monoclonal AP3. No reactions occurred in the absence of quinine (not shown). The sharp edges at the lateral margin of each band resulted from cutting the membrane into strips after protein transfer from a preparative gel.