Schematic view of the platelet GP Ib-IX-V complex. Key structural features of the complex are shown. The leucine-rich repeats of the four polypeptides are drawn based on the structure determined for the porcine ribonuclease inhibitor, a protein made up entirely of leucine-rich repeats.32 The depicted polypeptide arrangement is based on the published stoichiometry determined by monoclonal antibody binding17-19 and on the associations determined for the polypeptides.47,112 A caveat about this depiction: the quantity of GP V on the platelet surface has only been determined using 2 GP V monoclonal antibodies,18,20 which could lead to overestimates or underestimates of true polypeptide number. In addition, no quantitation has ever been performed to indicate that every GP V molecule on the platelet surface is associated with the complex. Complexes of greater complexity having the same stoichiometry are also possible.22 82 Diamonds on stalks represent N-linked carbohydrates and circles on stalks represent O-linked carbohydrate.