Midkine (MK) and the functionally-related protein pleiotrophin are heparin-binding neurotrophic factors that signal through the same receptor, known as anaplastic lymphoma kinase (ALK). MK plays an important regulatory role in epithelial-mesenchymal interactions during fetal development and in postnatal lung development. MK chemoattracts embryonic neurons, neutrophils and macrophages, and exerts angiogenic, growth and survival activities during tumorigenesis. Recombinant Human Midkine is a 13.4 kDa protein containing 123 amino acid residues including five intra-molecular disulfide bonds.