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Peptides are chemical chains formed by the joining of 2 to 50 amino acid molecules, the individual amino acid residues in the peptide chain being connected to each other by an amide type of covalent chemical bond called often as peptide bonds. Although the very idea of linking amino acids to a chain is more than 100 years old, it took another 50 years to find a solution to the resulting problems. The discovery of peptide synthesis has led to the development of a diverse and wide range of application in which synthetic peptides are successfully used today. In our offer you will find best peptides and proteins of highest possible quality and maximum purity. All is strictly tested, because maximum quality and customer satisfaction is most important to us.
Peptide synthesis is most often performed by condensing the carboxyl group of an incoming amino acid to the N-terminus of a growing peptide chain. This C-to-N synthesis is in contrast to natural protein biosynthesis, during which the N-terminus of the incoming amino acid is linked to the C-terminus of the protein chain (N-to-C). We know of two main methods of peptide synthesis, which are solid or liquid phase synthesis. In the most common solid phase peptide synthesis, the C-terminus is protected by attachment to a solid resin, which also simplifies the separation of the peptide from the reaction mixture. Synthesis of peptides in the liquid phase or synthesis in solution is slower and more demanding, but has the advantages of multiple purifications and the possibility of convergent synthesis, in which the synthesized peptides can be joined to form larger ones.
In addition to conventional basic peptide synthesis, advanced peptide modification options, structures, and properties are available today, including modifications such as phosphorylation, sulfonation, hydroxylation, palmitoylation, methylation, biotinylation, glycosylation, cyclization, or attachment to carrier proteins, and the like. These modifications can significantly alter or improve the properties of the resulting peptide.
The concept of solid phase peptide synthesis (SPPS) is to maintain the chemistry that has proven successful in solution, but to add a covalent attachment step that connects the resulting peptide chain to an insoluble polymeric carrier (resin). The anchored peptide is then extended by a series of addition cycles. The essence of the solid phase approach is that the reactions are driven to the end using excess soluble reagents, which can be removed by simple filtration and washing without handling losses. Upon completion of chain extension, the crude peptide is released from the support. With solid phase peptide synthesis (SPPS), it is possible to synthesize peptides up to 50 amino acids in length. A great advantage is also that this technology allows the incorporation of unnatural amino acids into the synthesis and the creation of unique peptides to optimize the desired and unique resulting properties.
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Peptides are chains formed by joining 2 to 50 amino acid molecules. The individual amino acids in the peptide chain are linked to one another by so called peptide bonds. Amino acid chains, which consist of more than 50 linked amino acid molecules, are already called proteins. Proteins consist of one or more polypeptides arranged in a biologically functional way. However, proteins can also be cleaved by enzymes (other proteins) into short peptide fragments. The term polypeptide refers to a longer, contiguous and unbranched peptide chain that does not specify exactly the number of amino acids from which it is made. In contrast, the designation oligopeptide represents a short peptide consisting of 2 to 20 amino acids.
Peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligosaccharides, polysaccharides, and others. In nature, the importance of peptides is irreplaceable, because they are found in all living organisms, where they play a key role in all types of biological activities. Synthetically designed peptides produced by laboratories, in turn, are often useful, for example, in peptide studies, in the production of antibodies and peptide hormones (or analogs thereof), or in the design of new enzymes and pharmaceutical drugs. Due to its excellent intrinsic properties, attractive pharmacological profile, specificity and usually low toxicity; what all translates into excellent safety, tolerability and efficiency, peptides represent an excellent starting point for new therapeutics development.
Peptides and Peptide bond
Peptide bond is an amide type of covalent chemical bond, that linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another amino acid. The formation of a peptide bond is a type of condensation reaction, that consumes energy (in live organisms, this energy is obtained from ATP). 2 amino acids approach each other, with the non-side chain (C1) carboxylic acid moiety of one coming near the non-side chain (N2) amino moiety of the other. One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH2). This reaction produces a molecule of water (H2O) and two amino acids joined by a peptide bond (-CO-NH-).
Amino acids that have been incorporated into peptides are termed amino acid residues. All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptid. The information that defines which amino acids formed the peptide and in which order they are linked by the peptide bond is called the amino acid sequence. Each peptide or protein has its own and unique sequence, and more than 100,000 different amino acid sequences of various peptides and proteins are currently already known and recorded.
Proteinogenic amino acids
Natural amino acids that combine into peptide and protein chains are called proteinogenic amino acids (or also marked as “standard” amino acids). About 500 naturally occurring amino acids are known, but only 22 of them are “proteinogenic”. Of these 22 protein amino acids, 20 are encoded by the universal genetic code; and there are a large number of their possible combinations, which can form many different peptides and proteins. 20 proteinogenic amino acids, which are encoded by the universal genetic code:
The genetic code is the set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences of nucleotide triplets, or codons) into peptides and proteins. In translation, messenger RNA (mRNA) is decoded in the ribosome decoding center to produce a specific amino acid chain, or polypeptide. The genetic code defines how codons specify which amino acid will be added next during peptide/protein synthesis. The genetic code is highly similar among all organisms.
Main Functions of Peptides and Proteins
The chemical and physical properties of a peptide are directly dependent on the amino acids that make up its structure, the sequence in which they are linked, as well as the specific shape of the peptide, or possible post-translational modifications. And just as their structure and resulting properties can vary greatly, so their effects and functions can be also very different. Peptides are synthesized in all living organisms – in humans, animals, plants, and perform many important tasks and irreplaceable functions. The most important functions of peptides in living organisms include:
- Neuropeptides serve neurons in the brain to communicate with each other
- Neurotropic peptides promote the growth, survival and differentiation of developing and mature neurons
- Peptide hormones act on the endocrine system and transmit signals between cells and glands (as biologic messengers)
- Cardiovascular peptides are secreted by the heart relative to cardiac transmural pressures
- Opioid peptides play a role in emotions, feelings, response to stress or pain, control of food intake, etc.
- Antimicrobial peptides are an important part of innate immune defense in many living organisms
- Anti-inflammatory peptides have anti-inflammatory properties, in multicellular organisms they form an important part of the immune system
- Gastrointestinal peptides control the functions of the digestive organs
- Peptides serve as structural components – they are the building blocks of proteins
- Peptides, as enzymes and biological catalysts, accelerate metabolic reactions
- Skin peptides are used in skin care
- Venom peptides are found in animal venoms
- Plant peptides regulate plant growth, development and reproduction
Peptides bind to cell surface receptors
Peptides, as potent signaling molecules, primarily mediate their biological effects in numerous physiological processes, by selectively binding to their specific (target) cell surface receptors (such as G protein-coupled receptors (GPCRs), enzyme-linked receptors, integrins, or ion channels). Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the plasma membrane of cells. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space.
Peptides (as extracellular molecules) by binding to their respective cell surface receptors, activate these receptors. This triggers cell signaling, the process of signal transduction. Signal transduction (also known as cell signaling) is the process by which a chemical or physical signals from the outside of a cell is transmitted to its interior, as a series of molecular events, that ultimately lead to a cellular response. One of the main functions of cell signaling is maintain normal physiological balance within the body. The extracellular molecules that bind and activate cell surface receptors include various peptides, proteins, hormones, neurotransmitters, cytokines, growth factors, cell adhesion molecules, or nutrients; which react with cell surface receptors to induce changes in the metabolism and activity of a cell.
Categories, classes and types of peptides
Peptides can be sorted, classified, or categorized according to many factors or their properties (such as chemical structure, their function, site of action, origin, and more), into many categories and groups. However, the types of peptides can often overlap, which means that a particular peptide can fall into several categories or belong to several types of peptides at the same time. Often, peptides are categorized according to the following factors and properties:
- By amino acid chain length; examples: Tetrapeptide is a peptide consisting of 4 amino acid residues; a hexa-peptide is a peptide consisting of 6 amino acid residues; an oligopeptide is a peptide consisting of 2 to 20 amino acid residues; a polypeptide is a simple linear peptide consisting of 21 to 50 amino acid residues.
- By structure; examples: Linear peptides are peptides that have a structure with a single linear sequence of peptide bonds;
cyclic peptides are peptides having a structure with a circular sequence of peptide bonds; peptides with secondary and tertiary structures (with three dimensional arrangements, where peptides chains are folded in space).
- By function; examples: Peptide hormones and endocrine peptides, neuropeptides, neurotropic peptides, cardiovascular peptides, gastrointestinal peptides, opioid peptides, lipopeptides, antimicrobial peptides, anti-inflammatory peptides.
- By source, origin or occurrence; examples: Naturally occurring peptides in human, animal or plant organisms, synthetically designed and manufactured peptides in laboratories, ribosomal peptides (assembled by ribosomes), nonribosomal peptides (assembled by enzymes), skin peptides (used in skin care).
Growth hormone-releasing peptides
One of the most important peptides for research is GHR peptides, due to their potential clinical use in the future. Growth hormone-releasing peptides (GHRPs) constitute a heterogeneous group of small synthetic peptides, whose primary function is to stimulate Growth hormone (GH) secretion by Somatotropic pituitary cells. These peptides trigger and stimulate the production of Growth hormone by mimicking the action of the natural peptide hormone Ghrelin. Ghrelin is the 28-amino-acid endogenous hormone with GH-releasing action secreted by gastric cells with orexigenic, cardioprotective, and cytoprotective abilities for a myriad of cell populations. GH-releasing peptides do not actually have sequence similarity to Ghrelin, however mimic Ghrelin by acting as agonists at the Ghrelin/Growth hormone secretagogue receptor (GHSR). Growth hormone-releasing peptides bind to two different receptors – GHS-R1a and CD36, through which they redundantly or independently exert relevant biological effects. The binding of Growth hormone-releasing peptides and Ghrelin mimetics to receptor GHS-R1a (Growth hormone secretagogue receptor transcript 1a) in pituitary cells, stimulates the secretion of Growth hormone by the pituitary gland. Growth hormone-releasing peptides impacts GHRH (Growth hormone releasing hormone) stimulation and Somatostatin (Growth hormone inhibiting hormone) inhibition via several pathways. Specifically, members of the GHRP secretagogue family stimulate pituitary Growth hormone production directly by 2- to 3-fold, oppose central nervous system and pituitary inhibition by Somatostatin, elicit arcuate nucleus release of GHRH into portal blood, synergize with GHRH, and induce pituitary GH gene expression. Receptor CD36 (Cluster of differentiation 36) activates prosurvival pathways such as PI-3K/AKT1, thus reducing cellular death.
In addition to these basic features, scientific research and clinical trials have also found other pharmacological effects of these peptides, which could be useful in the treatment of many diseases and medical conditions: Growth hormone-releasing peptides decrease reactive oxygen species (ROS) spillover, enhance the antioxidant defenses, and reduce inflammation. These cytoprotective abilities have been revealed in cardiac, neuronal, gastrointestinal, and hepatic cells, representing a comprehensive spectrum of protection of parenchymal organs. Antifibrotic effects have been attributed to some of the GHRPs by counteracting fibrogenic cytokines. Growth hormone-releasing peptides also have shown a potent myotropic effect by promoting anabolia and inhibiting catabolia. The myocardium has been shown to express functional GHRP receptors that appear to have distinct binding properties compared to the pituitary receptors. Increased CD36 expression probably also account for the cardioprotective effects of growth hormone-releasing peptides. GHRPs-mediated cardiotropic and cytoprotective effects are superior to those shown by the exogenous administration of GH and are not shared by GH-releasing hormone (GHRH) and that, importantly, growth hormone-releasing peptides exert their pharmacological actions via GH-independent pathways. Growth hormone-releasing peptides exhibit a broad safety profile in preclinical and clinical settings. Mounting evidences since the early 1980s has shown the unexpected pharmacological cardioprotective and cytoprotective properties of growth hormone-releasing peptides. However, despite intense basic pharmacological research, alternatives to prevent cell and tissue demise before lethal insults have remained as an empty niche in the clinical armamentarium. Growth hormone-releasing peptides are very hopeful for multiple pharmacological uses, especially as a myocardial reperfusion damage-attenuating candidate, and this family of “healing” peptides awaits further scientific research and a place in a clinical niche.