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/gp330. 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 e, Xenopus/Amphibian,tent of proteolytic fragmentation.