Lufaxin may interact simultaneously with proconvertase and prothrombinase. On an activated platelet, the open conformation of the proconvertase C3bB will normally be activated by fluid-phase FD. In the presence of lufaxin, the proconvertase is locked in the closed conformation and FB cannot be cleaved by FD. At the same time, lufaxin possibly also bridges the proconvertase with the prothrombinase fVa-fXa, and the latter is unable to cleave prothrombin because lufaxin blocks the active site of fXa.