Peptides Glossary

A chemical modification where the C-terminal carboxyl group of a peptide is replaced with an amide group (-CONH₂). This protects the peptide from degradation by carboxypeptidases and is found in many naturally occurring bioactive peptides.

The fundamental building blocks of peptides and proteins. There are 20 standard amino acids, each with a unique side chain (R-group) that determines its chemical properties. Amino acids are linked together by peptide bonds to form peptide chains.

A synthetic hexapeptide that mimics the N-terminal sequence of SNAP-25, a protein involved in neurotransmitter release. It is marketed as a topical "Botox alternative" that may reduce the depth of expression lines by partially inhibiting muscle contraction.

A form of cell signalling where a cell secretes a peptide or hormone that acts on receptors on the same cell. Contrasted with paracrine (acting on nearby cells) and endocrine (acting on distant cells via the bloodstream) signalling.

A protein that supports the survival, growth, and differentiation of neurons and synapses. Low BDNF is associated with depression, cognitive decline, and neurodegenerative diseases. Several peptides such as Semax upregulate BDNF expression.

The fraction of an administered dose that reaches the systemic circulation in an active form. Oral bioavailability of most peptides is very low (often <1%) because they are rapidly degraded by gastrointestinal proteases. Injection (subcutaneous or intramuscular) provides much higher bioavailability.

A solid-phase peptide synthesis strategy using tert-butyloxycarbonyl (Boc) as the N-terminal protecting group, removed with strong acid (TFA). Preferred for very long peptides or those containing difficult sequences. Largely superseded by Fmoc chemistry in modern labs.

A 15-amino acid peptide derived from a protective protein found in gastric juice. Extensively studied in animal models for its effects on wound healing, tendon and ligament repair, gut health, and anti-inflammatory activity. Not FDA-approved for human use.

The end of a peptide or protein chain that has a free carboxyl group (-COOH). By convention, peptide sequences are written from N-terminus (left) to C-terminus (right). SPPS builds peptides from the C-terminus upward.

A document from a manufacturer confirming the identity, purity, and quality of a peptide batch through specific analytical tests including HPLC purity percentage, mass spectrometry molecular weight, and endotoxin levels. Essential for verifying research peptide quality.

A synthetic analogue of growth hormone-releasing hormone (GHRH) with a modified sequence that resists enzymatic degradation. Available in two forms: without DAC (half-life ~30 minutes) and with DAC (half-life ~7 days due to albumin binding). Stimulates GH and IGF-1 release.

Short peptides derived from hydrolysed collagen protein, typically 2–10 amino acids in length. When applied topically or consumed orally, they may stimulate fibroblasts to produce new collagen. Common examples include Palmitoyl Tripeptide-1 (Pal-GHK) and Matrixyl.

A naturally occurring tripeptide (Gly-His-Lys) that binds copper ions. GHK-Cu is found in human plasma and has been extensively studied for wound healing, collagen synthesis stimulation, antioxidant activity, and anti-inflammatory effects in skin.

A peptide modification where the N- and C-termini (or two side chains) are covalently linked to form a ring structure. Cyclic peptides are highly resistant to proteolysis and often have improved receptor binding due to conformational rigidity.

Mirror-image (enantiomeric) forms of the standard L-amino acids found in proteins. Incorporating D-amino acids into a peptide sequence makes it resistant to proteases, which are stereospecific and cannot cleave D-amino acid bonds.

A chemical modification applied to CJC-1295 that adds a maleimidopropionic acid group, enabling the peptide to covalently bind to albumin cysteine-34 in the bloodstream. This extends the half-life from ~30 minutes to over 7 days.

A peptide consisting of exactly two amino acids joined by a single peptide bond. Examples include carnosine (beta-alanyl-L-histidine) and anserine. Some dipeptides have significant biological activity despite their small size.

The network of proteins and polysaccharides (including collagen, elastin, fibronectin, and hyaluronic acid) that provides structural support to cells in the skin and other tissues. Many skincare peptides target ECM production or protection.

Cell signalling where a peptide hormone is secreted into the bloodstream and travels to act on distant target cells bearing specific receptors. Examples include growth hormone (GH) secreted by the pituitary acting on liver and muscle cells.

A synthetic tetrapeptide (Ala-Glu-Asp-Gly) derived from the natural pineal peptide Epithalamin. Studied primarily by Russian scientists for its proposed telomerase-activating, antioxidant, and melatonin-regulating properties. Research chemical status in Western countries.

The primary cell type in the dermis (deep skin layer) responsible for producing collagen, elastin, and other ECM components. Fibroblast activity declines with age, leading to reduced collagen synthesis and skin thinning. Many anti-aging peptides target fibroblast stimulation.

The most widely used solid-phase peptide synthesis strategy, using 9-fluorenylmethoxycarbonyl (Fmoc) as the N-terminal protecting group, removed with mild base (piperidine). Compatible with most amino acids and allows real-time UV monitoring of deprotection.

The natural pattern of growth hormone (GH) secretion from the pituitary gland, which occurs in discrete pulses (primarily during deep sleep and after exercise) rather than continuously. GH secretagogues like Ipamorelin work by amplifying these natural pulses.

A copper-binding tripeptide (Gly-His-Lys) naturally found in human plasma, saliva, and urine. One of the most studied skincare peptides, with evidence for wound healing acceleration, collagen and glycosaminoglycan synthesis, and antioxidant activity.

A 44-amino acid hypothalamic peptide that stimulates the pituitary gland to synthesise and release growth hormone. CJC-1295 is a synthetic GHRH analogue. GHRH acts synergistically with ghrelin/GHS peptides to maximise GH release.

A class of peptides and small molecules that stimulate GH release by acting on the ghrelin receptor (GHSR-1a) in the pituitary and hypothalamus. Examples include Ipamorelin, GHRP-2, GHRP-6, and Hexarelin. They work synergistically with GHRH analogues.

A 191-amino acid peptide hormone secreted by the anterior pituitary gland. GH promotes muscle protein synthesis, fat lipolysis, bone growth, and stimulates IGF-1 production in the liver. GH secretion declines with age (somatopause).

The time required for the concentration of a drug or peptide in the body to be reduced by half. Most native peptides have very short half-lives (minutes) due to rapid proteolytic degradation. Chemical modifications like PEGylation, DAC, and cyclization extend half-life.

An analytical technique used to separate, identify, and quantify components in a mixture. Reverse-phase HPLC (RP-HPLC) is the gold standard for determining peptide purity (expressed as % area under the main peak) and for preparative purification of synthetic peptides.

The chemical breakdown of a molecule by reaction with water. Peptide bonds are susceptible to hydrolysis, which is why peptides are degraded by proteases (enzymes that catalyse peptide bond hydrolysis) in the body and in the gastrointestinal tract.

A 70-amino acid peptide hormone produced primarily in the liver in response to growth hormone stimulation. IGF-1 mediates many of GH's anabolic effects, promoting muscle protein synthesis, satellite cell activation, and anti-apoptotic signalling in muscle tissue.

A selective growth hormone secretagogue pentapeptide (Aib-His-D-2Nal-D-Phe-Lys-NH₂) that stimulates GH release with high selectivity for the GHSR-1a receptor. Unlike GHRP-6, it does not significantly increase cortisol or prolactin, making it one of the cleanest GHS peptides.

A pentapeptide (Tyr-D-Ala-Gly-Phe-Leu) that acts as an enkephalin analogue, modulating neuromuscular signal transmission to reduce muscle contraction and expression wrinkles. Often combined with Argireline for synergistic anti-wrinkle effects.

The attachment of fatty acid chains to a peptide, improving its binding to albumin in the bloodstream and extending circulation time. Semaglutide (Ozempic) uses C18 fatty acid lipidation to achieve its once-weekly dosing profile.

An analytical technique that measures the mass-to-charge ratio of ions to determine the molecular weight and structure of a compound. Used to confirm the identity of synthetic peptides by verifying their exact molecular weight matches the theoretical value.

A palmitoylated pentapeptide (Pal-Lys-Thr-Thr-Lys-Ser) that is one of the most clinically studied cosmetic peptides. It mimics a collagen breakdown fragment, signalling fibroblasts to increase collagen, elastin, and hyaluronic acid production. Matrixyl 3000 combines Matrixyl with Palmitoyl Tripeptide-1.

A family of enzymes that degrade ECM components including collagen and elastin. MMP activity increases with UV exposure and ageing, contributing to skin wrinkling and sagging. Some peptides inhibit MMPs (e.g., Tripeptide-10 Citrulline) to protect skin structure.

A central protein kinase that integrates nutrient, energy, and growth factor signals to regulate protein synthesis, cell growth, and autophagy. IGF-1 and insulin activate mTOR, which is the primary driver of muscle protein synthesis and hypertrophy.

The end of a peptide or protein chain that has a free amino group (-NH₂). By convention, peptide sequences are written from N-terminus (left) to C-terminus (right). The N-terminus is often the site of chemical modifications to improve stability.

A peptide that acts as a neurotransmitter or neuromodulator in the nervous system. Examples include substance P, enkephalins, and neuropeptide Y. In skincare, neuropeptides like Argireline target neuromuscular junctions to reduce expression wrinkles.

A peptide containing a small number of amino acids, typically 2–20. The term is used loosely in cosmetics to describe short peptides used in skincare formulations. Oligopeptides are small enough to potentially penetrate the stratum corneum.

The attachment of a palmitic acid (C16 fatty acid) chain to a peptide, improving its ability to penetrate the lipid-rich stratum corneum of the skin. Most cosmetic peptides (e.g., Matrixyl, Argireline) are palmitoylated to enhance skin penetration.

The covalent attachment of polyethylene glycol (PEG) chains to a peptide or protein. PEGylation reduces renal clearance (by increasing molecular size above the glomerular filtration threshold), shields from proteases, and dramatically extends circulating half-life.

A short chain of amino acids (typically 2–50) linked by peptide bonds. Peptides are smaller than proteins and can act as hormones, neurotransmitters, enzymes, and signalling molecules. The boundary between peptides and proteins is conventionally set at ~50 amino acids.

The covalent chemical bond formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH₂) of the next, with the loss of a water molecule. The peptide bond is planar and partially double-bond in character, restricting rotation.

The study of how a drug moves through the body — encompassing absorption, distribution, metabolism, and excretion (ADME). Key PK parameters for peptides include bioavailability, half-life, volume of distribution, and clearance rate.

A small endocrine gland at the base of the brain that produces and secretes numerous peptide hormones, including growth hormone (GH), TSH, FSH, LH, ACTH, and prolactin. The anterior pituitary is the primary target of GHRH and GHS peptides.

An enzyme that catalyses the hydrolysis of peptide bonds, breaking down peptides and proteins. The body contains numerous proteases (e.g., trypsin, chymotrypsin, dipeptidyl peptidase IV) that rapidly degrade most native peptides, limiting their half-life.

A large polypeptide chain (typically >50 amino acids) that folds into a specific three-dimensional structure to perform biological functions. Proteins differ from peptides primarily in size and the complexity of their folded structures.

A protein molecule (typically on a cell surface or inside a cell) that specifically binds to a peptide or other signalling molecule, triggering a cellular response. The specificity of peptide-receptor interactions determines the biological effects of a peptide.

A synthetic analogue of the endogenous peptide tuftsin, extended with a stabilising sequence. Approved in Russia as an anxiolytic and nootropic. Modulates GABAergic signalling, serotonin metabolism, and enkephalin degradation without causing sedation or dependence.

A synthetic heptapeptide analogue of the ACTH 4-7 fragment, approved in Russia for stroke recovery and cognitive impairment. Proposed mechanisms include BDNF and NGF upregulation, and modulation of dopaminergic and serotonergic systems.

A class of cosmetic peptides that act as chemical messengers, signalling skin cells (particularly fibroblasts) to increase production of collagen, elastin, and other structural proteins. Matrixyl and GHK-Cu are the most studied signal peptides in skincare.

The dominant method for producing synthetic peptides, developed by R. Bruce Merrifield (Nobel Prize 1984). Peptides are assembled one amino acid at a time while anchored to a solid resin support, building from the C-terminus to the N-terminus.

Peptides in which a synthetic hydrocarbon bridge (staple) is inserted between two amino acid side chains, locking the peptide in its bioactive helical conformation. Stapled peptides show improved protease resistance, cell membrane penetration, and binding affinity.

The outermost layer of the skin, composed of dead, flattened keratinocytes embedded in a lipid matrix. It acts as the primary barrier to topical drug penetration. Most cosmetic peptides require palmitoylation or other modifications to penetrate this layer effectively.

A synthetic version of the naturally occurring peptide Thymosin Beta-4, a 43-amino acid protein involved in actin polymerisation, cell migration, wound healing, and angiogenesis. Studied for tendon, ligament, and muscle injury recovery. Not FDA-approved for human use.

An enzyme that adds repetitive DNA sequences (TTAGGG) to the ends of chromosomes (telomeres), counteracting the shortening that occurs with each cell division. Telomere shortening is a key hallmark of cellular ageing. Epithalon is proposed to activate telomerase.

Repetitive DNA sequences at the ends of chromosomes that protect them from degradation and fusion. Telomeres shorten with each cell division and with oxidative stress. When telomeres become critically short, cells enter senescence or apoptosis.

A peptide consisting of exactly three amino acids joined by two peptide bonds. Many biologically active tripeptides exist, including GHK (Gly-His-Lys, the copper-binding peptide), glutathione (Glu-Cys-Gly), and thyrotropin-releasing hormone (TRH).

The international organisation that sets and enforces anti-doping rules in competitive sport. WADA's Prohibited List S2 bans all peptide hormones, growth factors, and related substances including GHS peptides, IGF-1, and growth hormone. Updated annually.

A class of peptides that accelerate tissue repair by promoting angiogenesis (new blood vessel formation), fibroblast migration, collagen synthesis, and anti-inflammatory signalling. Key examples include BPC-157, TB-500 (Thymosin Beta-4), and GHK-Cu.