Human Midkine (MK) is a new member of the heparin-binding neurotrophic factor family. MK and PTN (Pleiotrophin) are structural homologs, and are highly conserved among species. MK plays important roles in development and carcinogenesis and has several important biological effects, including promotion of neurite extension and neuronal survival. Human midkine is a 13.4 kDa protein, comprising of 123 amino acid residues.