during the early events of coagulation of human blood by the intrinsic pathway , factor xii is activated to a form which can activate factor xi , and is proteolytically fragmented to smaller species ( 30,000 daltons and 70,000 daltons ) which have lost most of the ability to activate factor xi but which can activate prekallikrein rapidly .
C0005778
coagulation
C0015525
factor xii