Emil Fischer discovered the first synthetic peptide glycyl-glycine in 1901, in partnership with Ernest Fourmeau. However, Vincent du Vigneaud synthesized the first polypeptide (oxytocin-nine amino acid sequence) in 1953. Peptides are chemical compounds that consist of at least 2 amino acids (amino polymers), that are joined by a peptide bond. This is when the nitrogen atom of one of the amino acids binds to the carboxyl carbon atom of another amino acid. Peptides are very similar to proteins in the sense that all molecules that are small enough to be synthesized from amino acids are referred to as peptides as opposed to proteins. That means proteins are simply another chain of amino acids, as are peptides. Peptides and proteins are separated by plus or minus 50 amino acids. Molecules that contain between 50 to 50 amino acids are thus referred to as peptides, whilst molecules that contain more than 50 amino acids are referred to as proteins. Furthermore, molecules whose weight ranges from 1000s to millions of daltons (D) are called polypeptides. Polypeptides can be described as continuously long peptides. Polypeptides are so similar to proteins that their names are often changed around to refer to the same thing. Peptides are listed under the wide-ranging chemical class of biological oligomers and polymers, together with polysaccharides, oligosaccharides and nucleic acids. Peptides can also be referred to as dipeptides, tripeptides, tetra peptides, oligopeptides and so forth, depending on the quantity of amino acids found in each.
Within our bodies, peptides function as regulators of the activity of several of our systems by intermingling with target cells. That is why some peptides are found in our hormones, whilst others are within our immune systems, and others are cell-communicating substances that inform our cells the manner in which they should react, as well as what to do. Some peptides contribute towards wound healing, and others contribute towards the pathology of skin conditions such as eczema. However, further research is still being conducted concerning the full uses of peptides when it concerns their activities in our bodies.
Peptides are used for a wide variety of reasons in medicinal and biotechnology research. They control most of the physiological processes, as endocrine or paracrine signals as well as neurotransmitters also known as growth factors. There are at least 60 peptide drugs that have been approved for sale on the market by the FDA. 140 drugs are in the trial process and well over 500 are in pre-clinical development. During the research of how to treat diabetes, the first therapeutic protein to be introduced as a solution was insulin in the 1920s.
A number of peptides are used for diagnostic purposes, for example C-peptide is used to monitor insulin production and to help determine the cause of low blood sugar (hypoglycemia).
Peptides are synthesized by coupling the carboxyl group or C-terminus of one amino acid to the amino group or N-terminus of another. There are two strategies for peptide synthesis: liquid-phase peptide synthesis and solid-phase peptide synthesis (SPPS).
Peptides are divided into several classes, depending on how they are produced:
Milk Peptides are formed from casein, as a result of this milk protein (casein) being broken down by digestive enzymes. They can also be formed during the fermentation process of milk, by lactobacilli.
Ribosomal peptides are synthesized by translation of mRNA. However, in order to produce the mature form, they have to be exposed to proteolysis. They function in hormones as well as signaling molecules. Some organisms manufacture peptides as antibiotics, for example microcins.
Non-ribosomal peptides are created by enzymes, that are unique to each peptide. The most common is known as glutathione. Glutathione is a component of antioxidant defenses of several aerobic organisms. Other non-ribosomal peptides are found mostly in unicellular organisms, fungi and plants. These ones are normally synthesized by modular enzyme complexes known as non-ribosomal peptide synthetases.
Peptones or Tryptones are extracted from animal milk or meat digested by proteolysis. They are normally used for the purpose of growing bacteria and fungi.
Peptide fragments are fragments of proteins that researchers use to be able to trace the source protein. They can be formed by the degradation of natural effects, or they can be manufactured in the laboratory, by deliberate enzymatic degradation.