LPA: lipoprotein, Lp(a). Apo(a) is the main constituent of lipoprotein(a) (lp(a)). It has serine proteinase activity and is able of autoproteolysis. Inhibits tissue-type plasminogen activator 1.Lp(a) may be a ligand for megalin/gp 330.Apo(a) is known to be proteolytically cleaved, leading to the formation of the so-called mini-lp(a).Apo(a) fragments accumulate in atherosclerotic lesions,where they may promote thrombogenesis.O-glycosylation may limit the extent of proteolytic fragmentation.