Human growth hormone (HGH) is nonglycosylated protein is secreted from pituitary anterior lobe. The hGH containing 2 intramolecular disulfide bonds has 22,000 dalton of molecular weight. It is initially synthesized as a precursor and is secreted from the cell after processing. The hGH is produced in large quantities before adulthood, and is produced during a whole human life. Growth hormone acts through binding to membrane receptors that belong to the cytokine receptor superfamily. Ligand binding induces receptor dimerization and activation of the receptor-associated kinase JAK-2, resulting in phosphorylation of the kinase, the receptor and many cellular proteins. The hGH is necessary for normal growth and development, but several types of dwarfism are caused by the abnormal low-level production of hGH and the over production of hGH can be accompanied by acromegaly or gigantism. Human growth hormone (hGH) stimulates the liver to produce somatomedin-1, which in turn causes growth of muscle and bone; stimulation of fat, muscle and cartilage cell differentiation, as well as affecting lipid and carbohydrate metabolism. Analogues of growth hormone are also known in other species, and any mammalian growth hormone (GH) or derivative thereof may be used. There are variant forms of human growth hormone (hGH) which include a disulfide dimer, a glycosylated form (20 kD hGH) and two pituitary peptides made up of portions of 22 kD hGH. The two pituitary peptides have, respectively, insulin-potentiating and anti-insulin properties. The smaller peptide may be useful in decreasing the amount of exogenous insulin required by diabetics, whereas the larger peptide may be involved in diabetic retinopathy.
Growth hormone, a polypeptide hormone, is synthesised in the anterior lobe of the pituitary gland as a larger precursor molecule. In nature the precursor molecule is processed by cleavage to yield the biologically active form of the hormone. The administration of HGH is known to decrease the body's sensitivity to insulin, thus causing a compensating rise in pancreatic insulin output and therefore in serum insulin levels; yet paradoxically, falling HGH levels in aging humans are accompanied by increasing serum insulin levels. The precursors are compounds which are converted into the peptides in the human body. A polypeptide is a polymer of amino acid residues joined by peptide bonds, whether produced naturally or synthetically. Polypeptides of less than about 10 amino acid residues are commonly referred to as peptides. A protein is a macromolecule comprising one or more polypeptide chains. A protein may also comprise non-peptidic components, such as carbohydrate groups. Carbohydrates and other non-peptidic substituents may be added to a protein by the cell in which the protein is produced, and will vary with the type of cell. A protein consisting of, for example, from 15 to 1500 amino acid residues may further contain one or more carbohydrate chains. hGH is a protein of 191 amino acids produced in the anterior lobe of the hypophysis throughout the life of an individual, and in greater quantities during the preadult period. The growth hormone is synthesised in the form of a precursor and, once processed is secreted from the cell. Recombinant DNA techniques are known for the preparation of polypeptides fused to an amino acid sequence which can be divided specifically in vitro by enzymatic hydrolysis. Human growth hormone (hGH) may be prepared from soluble precursors by hydrolysis of the precursors with an enzyme. The enzymatic hydrolysis is carried out by the addition of an enzyme to the proteic solution containing the precursor for the purified hGH and the separation of the mature hGH thus obtained from the reaction mixture. |
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