Growth Hormone
Growth hormone or somatotrophin is a naturally occuring peptide hormone, a polypeptide or small protein that contains a single chain polypeptide which amino acid sequence is made up of 191 amino acids. The three-dimensional structure is stabilized by two disulfide bridges and has four helical structures. The position of the helices and the overall three-dimensional structure of this hormone are important for receptor binding. The hormone shares structural homologies with prolactin and human chorionic somatomammotropin (hCS). HCS is a growth hormone variant synthesized exclusively in the placenta. The hormone circulating in the body is rather heterogeneous.
There is a cluster of five genes from which these polypeptide hormones may be synthesized but normally only one gene expressed tissue-specifically. Binding of the tissue-specific transcription factor Pit-1 to the promoter region of the growth hormone gene results in only one form of growth hormone that are secreted by the anterior pituitary gland.