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. A specific inhibitor of endothelial cell growth and angiogenesis. Displays increased inhibitory activity (ED₅₀ =70 nM) relative to kringles 1-4 (ED₅₀ = 135 nM). Ang K1-3 reduces endothelial cell proliferation and acts as a potent inhibitor of angiogenesis and tumor growth.