Peptides are molecules whose amino acids are linked by peptide bonds. They perform numerous functions and, in addition to hormonal effects, can have pain-relieving or anti-inflammatory effects, for example. Because of their numerous tasks, peptides are now used as active ingredients in medicines.
What is a peptide?
Proteins are macromolecules made of amino acids. In this sense, the peptide can also be called a protein. Peptides contain peptide bonds of amino acids. These peptide bonds correspond to amide-like bonds between the α-carbon atom amino group and the carboxy group of two amino acids. Peptides differ from true proteins in molar mass. The number of all linked amino acids in a peptide is therefore not equal to the number of the same in a protein. Nevertheless, there is a fluid distinction between proteins and peptides. The term protein is usually used for amino groups of more than 100 amino acids. Anything below that is more commonly referred to as a peptide. The term peptide was coined by Emil Fischer in the early 20th century. He used the term in reference to peptone and thus the protein degradation products of pepsin, adding the ending of polysaccharide to the new term because of the similarity in construction to monomers. Systematically, peptides are subdivided according to the number of amino acids. Oligopeptides, for example, contain fewer than ten amino acids. Polypeptides contain up to 100, and cyclopeptides contain at least two amino acids in ring structure.
Function, effect, and tasks
Peptides perform a wide range of physiological functions in the body, which vary with the type and structure of the peptide form. For example, they can act in a hormone-like manner or exert anti-inflammatory effects. They also take on pro-inflammatory effects. The same applies to antibiotic or antiviral active functions. Some peptides regulate Stoffwechsel processes. Growth and pain empfindence are also linked to peptides. All peptide substances in the body are highly active and have highly specific activity. As calcitonin, for example, they lower calcium levels in the thyroid gland. As endorphins, they are found in many organs to reduce pain. As glucagon in the pancreas, they are involved in glucagen degradation. As insulin, they are also present in the pancreas and are involved in glucose uptake. In the form of parathyroid hormone, they are found in the parathyroid gland and mobilize calcium for bone formation. As somasostatin, they also regulate growth processes and hormone effects in various organs. They are equally important as neurotransmitters and vasilidators. Opioidene peptides act like morphine and appear to support physical and mental development.
Formation, occurrence, properties, and optimal levels
Amino acids are always arranged in a defined sequence in a peptide and usually correspond to a linear chain. The number of amino acids in a peptide is called the chain length. Depending on this chain length and arrangement, peptides are either olgio-, poly-, and cyclo-peptides. There are α-peptide bonds, ω-peptide bonds and isopeptides. Circularly cross-linked peptides are cyclopeptides. During transcription, peptides are formed from α-amino acids in L-form. This process makes use of genetically encoded amino acids. Occasionally, D-amino acids can occur in peptides that are products of specific metabolic pathways and thus are not biosynthetic products. The synthesis of polypeptide chains is carried out by ribosomes. In addition, there is non-ribosomal peptide synthesis, which is performed enzymatically by peptide synthetases. Some dietary proteins are also processed into opioid peptides by digestive processes. The carboxy group of one amino acid reacts with the amino group of another amino acid during condensation with the escape of water to form an acid amide grouping, also known as -CO-NH-. The amide bond attached between a nitrogen atom and a carbon atom of the carbonyl group in question then transforms into a peptide bond. Peptide bonds are not free in their extensibility because two structures of resonance are present.
Diseases and disorders
Modern medicine applies peptides as drugs in the context of various diseases. For example, the substances have been used for many years in the context of cancer therapy.Currently, for example, peptides are used in this context that appear as conjugates on cytotoxic molecules. These peptides track down tumors and deliver a cytostatic to the tumor to kill the cells locally. This therapy is a gentler and locally applicable alternative to conventional chemotherapy. Peptides are also used in therapeutic vaccines. This therapeutic option involves the immunological presentation of antigen surfaces and their fragments. The immune system then forms specific antibodies to neutralize the presented antigen. Many antigens have a proteinogenic structure. The replication of peptides and their use in vaccines lends itself primarily for this reason. Peptides can be used as vaccines against various epidemics as well as against allergies. As highly active specific agents, peptides are thus used in a wide variety of drugs. Thanks to their biologically diverse functions, they can be used in a wide variety of applications. They have also established themselves as drugs against diabetes or obesity. The same applies in connection with cardiovascular or neurodegenerative diseases, for organ insufficiencies or as an alternative to antibiotics. Oral administration is not particularly effective because of rapid digestion. Therefore, the drug is usually given parenterally. Injection and depot formulations with a duration of action of several days are now used as well as nasal applications. Given their diverse modes of action, peptide-based diseases or mutations have a correspondingly wide range of symptoms. In the current era, however, many of these diseases can be treated relatively well due to advances in artificial peptide synthesis.
