Urokinase is a serine protease involved in degradation of the extracellular matrix and possibly tumor cell migration and proliferation. A specific polymorphism in the Urokinase gene may be associated with late onset Alzheimer disease and also with decreased affinity for fibrin binding. This protein converts plasminogen to plasmin by specific cleavage of an Arg Val bond in plasminogen. The proprotein is cleaved at a Lys Ile bond by plasmin to form a two chain derivative in which a single disulfide bond connects the amino terminal A chain to the catalytically active, carboxy terminal B chain. This two chain derivative is also called HMW uPA (high molecular weight uPA). HMW uPA can be further processed into LMW uPA (low molecular weight uPA) by cleavage of chain A into a short chain A (A1) and an amino terminal fragment. LMW uPA is proteolytically active but does not bind to the uPA receptor.