Human Pleiotrophin (PTN) also called HARP (Heparin affin regulatory peptide) is a new member of the heparin-binding neurotrophic factor family. PTN (Pleiotrophin) and MK (midkine) are structural homologs, and are highly conserved among species. PTN plays an important role in development processes and promotion of neurite extension. Recombinant human PTN is a His-tag fusion protein (17.3 kDa) containing 136 amino acid residues of the PTN.