Schematic representation of how FVIIIa and ACE910/emicizumab promote FXa generation. Comparison of the various differences in the interactions with enzyme and substrate between FVIIIa and ACE910/emicizumab. In the left panel, FVIIIa is bound to the phospholipid surface only by its C2 domain.^53,54  Other models predict that also the C1 domain may contribute directly to phospholipid binding (eg, see Meems et al⁵⁵ ).