Ang K1-3 is a single, non-glycosylated polypeptide chain containing 259 amino acids. It represents a proteolytic fragment of plasminogen containing the first three kringle structures. Ang K1-3 reduces endothelial cell proliferation and acts as a potent inhibitor of angiogenesis and tumor growth. It displays increased inhibitory activity(ED?? =70 nM) relative to kringles 1-4(ED?? = 135 nM).