Prothrombinase wani hadadden enzyme ne wanda ke haifar da jujjuyawar prothrombin zuwa thrombin, muhimmin mataki a cikin cascade na toshewar jini. An samo kalmar daga "prothrombin," furotin na farko da aka samar a cikin hanta, da "ase," wani kari da ake amfani da shi don nuna enzymes. Prothrombinase ya ƙunshi abubuwa da yawa, ciki har da factor Xa, factor Va, da calcium ions, waɗanda ke aiki tare don kunna prothrombin.