PTHrP is a polypeptide hormone produced by almost every tissue of the body. PTHrP is closely related to parathyroid hormone (PTH), which is secreted from the parathyroid gland, and plays a central role in regulating the extracellular concentrations of calcium and phosphorous. Recombinant human PTHrP is a 9.8 kDa linear polypeptide of 86 amino acid residues.