Peptide hormone growth hormone, which acts on bone, muscle, and the liver. The posterior pituitary gland secretes antidiuretic hormone, also called vasopressin, and oxytocin. The parathyroid gland secretes parathyroid hormone, the main hormone responsible for regulating serum calcium and phosphorus levels. Peptide hormones are also produced by many different organs and tissues, including the heart (atrial-natriuretic peptide (ANP) or atrial natriuretic factor (ANF)) and pancreas (glucagon, insulin and somatostatin), the gastrointestinal tract (cholecystokinin, gastrin), and adipose tissue stores (leptin). Peptide hormone Peptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain
Insulin suggests that it has been conserved across much of animal evolutionary history. The C-peptide of proinsulin (discussed later), however, differs much more among species; it is also a hormone, but a secondary one. The primary structure of bovine insulin was first determined by Frederick Sanger in 1951. After that, this polypeptide was synthesized independently by several groups. The 3-dimensional structure of insulin was determined by X-ray crystallography in Dorothy Hodgkin's laboratory in 1969 (PDB file 1ins). Insulin is produced and stored in the body as a hexamer (a unit of six insulin molecules), while the active form is the monomer.