Proteins and peptides are generally high molecular weight substances, each having a specific sequence of amino acids. Except for the smaller peptides, chemical synthesis of peptides and proteins is frequently impractical, costly and time consuming, if not impossible. The production and isolation of desired proteins by recombinant techniques, for example, employing genetically engineered or isolated gene sequences, has in recent years reached a moderate level of sophistication. Recombinant describes a nucleic acid molecule (polynucleotide) of genomic, cDNA, semisynthetic, or synthetic origin which, by virtue of its origin or manipulation is not associated with all or a portion of the polynucleotide with which it is associated in nature and/or is linked to a polynucleotide other than that to which it is linked in nature. Recombinant DNA techniques have recently made it possible to cause microorganisms as the host to express foreign genes and therefore desired foreign gene products can be produced by using these techniques.
Recombinant human proteins have become important pharmaceuticals. Proteinaceous molecules such as enzymes, hormones, storage proteins, binding proteins, transport proteins and signal transduction proteins may be produced and purified using various recombinant DNA techniques. Recombinant proteins are becoming widely accepted treatments for a number of human diseases. The combination of recombinant DNA technology and large-scale processes has enabled production of proteins that might otherwise have been impossible or too expensive to obtain from natural sources. For instance human growth hormone (hGH), immune interferon, tissue plasminogen activator (tPA) and human insulin are now commercial available by recombinant DNA technology.
Human growth hormone (HGH) or somatotropin is a globular polypeptide of 191 amino acids without sugar residues, with a molecular weight of approximately 22 kDa. Growth hormone (GH) produced in the anterior pituitary dramatically affects the phenotype of mammals since it determines the size of the individual. Human growth hormone has medical utility in the treatment of defective pituitary function. GH enhances protein synthesis, lypolysis, and epiphyseal growth, and is implicated in the regulation of the immune system. Growth hormone increases circulating insulin-like growth factor I (IGF-1) levels, which in turn, mediates growth in the liver and peripheral tissues. With the advent of recombinant DNA technology, the controlled microbial production of an enormous variety of useful polypeptides has become possible. Already in hand are bacteria modified by this technology to permit the production of such polypeptide products such as human growth hormone. Human Growth hormone preparations have been prepared from human pituitaries, but nowadays the products on the market are produced by recombinant methods, rhGH. Recombinant GH therapy is currently used in clinics AS prescription medication. Generally recombinant HGH has an extra methionine residue which is added at the N-terminus during protein synthesis by initiation codon although natural type HGH is composed of 191 amino acids without the methionine. Thus the recombinant HGH is produced as a form of methionyl HGH which is composed of 192 amino acids. Methionyl HGH exhibits the same activity with that of natural type HGH. |
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