title: Trypsin activation of human factor XI.
abstract: Human factor XI circulates as a zymogen composed of two similar or identical chains of Mr = 80,000. Upon activation either by trypsin or by blood-clotting proteins involving clotting factors XII and high molecular weight kininogen, it undergoes proteolytic cleavage in which the Mr = 80,000 chain reportedly is cleaved to a heavy and light chain of Mr of about 48,000 and 33,000, respectively. In these studies, we have reinvestigated trypsin activation of factor XI and demonstrate that trypsin-activated factor XI contains three chains of apparent Mr = 46,000, 37,000, and 26,000. Kinetic studies lead to the conclusion that the parent chain of Mr = 80,000 is cleaved into chains of Mr = 46,000 and 37,000. This cleavage is followed by a second nondestructive cleavage, most probably of the chain of Mr = 46,000, to yield the third product which migrates as a band of Mr = 26,000.
mesh_terms: D004789:Enzyme Activation; D005172:Factor XI / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D014357:Trypsin / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D005172:Factor XI; D014357:Trypsin