Scientific Glossary

The addition of an acetyl group (CH₃CO-) to a molecule. N-terminal acetylation is a common peptide modification that can increase stability and mimic natural post-translational modifications.

A molecule that binds to a receptor and activates it, producing a biological response. Peptide agonists mimic the action of endogenous signaling molecules.

A common secondary structure in peptides and proteins where the polypeptide backbone coils into a right-handed helical shape, stabilized by hydrogen bonds.

The conversion of a C-terminal carboxyl group (-COOH) to an amide group (-CONH₂). Many bioactive peptides are naturally amidated, enhancing receptor binding and stability.

An organic molecule containing both an amino group (-NH₂) and a carboxyl group (-COOH). The 20 standard amino acids are the building blocks of peptides and proteins.

Having both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. Many antimicrobial peptides are amphipathic, allowing membrane interaction.

The formation of new blood vessels from pre-existing vessels. Several peptides like BPC-157 and TB-500 are studied for their effects on angiogenic processes.

A molecule that binds to a receptor without activating it, blocking the action of agonists. Peptide antagonists are used to study receptor function and as therapeutics.

A peptide with activity against microorganisms (bacteria, fungi, viruses). AMPs are part of innate immune defense in many organisms.

Also known as: AMP

Advanced Obesity Drug, a modified fragment of human growth hormone (HGH 176-191) researched for fat metabolism and weight loss without the growth-promoting effects of full HGH.

Sterile water containing 0.9% benzyl alcohol as a preservative. Used to reconstitute peptides, allows multiple withdrawals from a vial while preventing bacterial growth.

Also known as: BAC Water, Bac Water

Brain-Derived Neurotrophic Factor, a protein that supports neuron survival, growth, and synaptic plasticity. Several nootropic peptides like Semax increase BDNF levels.

A secondary structure where polypeptide segments align side-by-side, connected by hydrogen bonds. Can be parallel or antiparallel orientation.

A peptide that exerts a biological effect on cells, tissues, or organisms. May be derived from food proteins or produced synthetically for research.

The proportion of an administered substance that reaches systemic circulation and is available for biological activity. Peptides often have limited oral bioavailability due to digestive breakdown.

The end of a peptide chain with a free carboxyl group (-COOH). By convention, peptide sequences are written with the C-terminus on the right.

Also known as: Carboxy Terminus, COOH Terminus

A synthetic analog of Growth Hormone Releasing Hormone (GHRH) that stimulates growth hormone release. Available with or without Drug Affinity Complex (DAC).

A peptide in which the chain forms a ring structure through a bond between the N- and C-termini or through side chain linkages. Often more stable than linear peptides.

The mirror image (enantiomer) of the naturally occurring L-amino acid. D-amino acids in peptides confer resistance to protease degradation.

A unit of molecular mass equal to one-twelfth the mass of a carbon-12 atom. Peptide molecular weights are typically expressed in Daltons (Da) or kiloDaltons (kDa).

Also known as: Da, kDa

A liquid used to dissolve or dilute a substance. For peptides, bacteriostatic water or sterile water are common diluents for reconstitution.

A peptide consisting of exactly two amino acids joined by one peptide bond.

A covalent bond formed between the sulfur atoms of two cysteine residues (-S-S-). Disulfide bonds stabilize peptide and protein structure.

Delta Sleep-Inducing Peptide, a neuropeptide researched for its effects on sleep regulation, particularly deep sleep phases.

Also known as: Delta Sleep Inducing Peptide

Half-maximal effective concentration. The concentration of a substance that produces 50% of its maximal effect, used to characterize peptide potency.

Originating from within an organism. Endogenous peptides are naturally produced by the body.

A synthetic tetrapeptide (Ala-Glu-Asp-Gly) studied for its effects on telomerase activation and potential anti-aging properties.

Also known as: Epitalon

An amino acid that cannot be synthesized by the organism and must be obtained from diet. Humans have nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Also known as: EAA

Originating from outside an organism. Exogenous peptides are administered externally or derived from dietary sources.

Fluorenylmethyloxycarbonyl, a protecting group used in solid-phase peptide synthesis. Fmoc chemistry is the most common modern SPPS approach.

Glucagon-Like Peptide-1, a hormone that stimulates insulin secretion and reduces appetite. GLP-1 agonists like semaglutide are used for diabetes and weight loss.

Also known as: Glucagon-Like Peptide-1

G-Protein Coupled Receptor, a large family of cell surface receptors that transduce signals via G-proteins. Many peptide hormones act through GPCRs.

Also known as: G-Protein Coupled Receptor

A peptide hormone secreted by the pituitary gland that stimulates growth, cell reproduction, and regeneration. Also known as somatotropin or HGH.

Also known as: HGH, Somatotropin, GH

The time required for half of a substance to be eliminated or degraded. Peptide half-lives are often short due to proteolytic degradation, ranging from minutes to days depending on the peptide.

Water-loving – molecules or regions that interact favorably with water. Polar and charged amino acids are hydrophilic.

Water-fearing – molecules or regions that avoid water. Nonpolar amino acids like leucine, isoleucine, and valine are hydrophobic.

Half-maximal inhibitory concentration. The concentration of an inhibitor that reduces activity by 50%, used to characterize antagonist potency.

Insulin-like Growth Factor 1, a hormone similar in structure to insulin that plays a key role in growth and has anabolic effects.

Also known as: Insulin-like Growth Factor 1

In glass – experiments performed outside living organisms, typically in test tubes, dishes, or cell culture systems.

In the living – experiments performed within living organisms (animal or human studies).

Administration of a substance into muscle tissue, typically using a needle. Some peptides are administered intramuscularly for slower absorption.

Also known as: IM

Administration through the nasal mucosa. Some peptides like Semax and Selank are administered intranasally for direct CNS access.

A selective growth hormone secretagogue that stimulates GH release without significantly affecting cortisol or prolactin. Often combined with CJC-1295.

The pH at which a molecule has no net electrical charge. Important for peptide purification and characterization.

Also known as: pI

A tripeptide (Lys-Pro-Val) derived from alpha-MSH with potent anti-inflammatory properties. Researched for gut inflammation and skin conditions.

The naturally occurring stereoisomer of amino acids found in proteins. The 'L' refers to the absolute configuration around the alpha carbon.

A molecule that binds to a receptor or other protein. Peptide ligands include hormones, neurotransmitters, and growth factors.

A human cathelicidin antimicrobial peptide with broad-spectrum activity against bacteria, viruses, and fungi. Also has immunomodulatory effects.

Also known as: Cathelicidin

Freeze-drying – removal of water from frozen samples under vacuum. Standard method for peptide storage and shipping that preserves stability.

Also known as: Freeze-Drying

An analytical technique that measures mass-to-charge ratios of ions. Essential for peptide identification, sequencing, and purity analysis.

Also known as: MS

A family of peptide hormones derived from proopiomelanocortin (POMC) that act on melanocortin receptors (MC1R-MC5R). Involved in pigmentation, appetite, and sexual function.

Synthetic analogs of alpha-MSH that stimulate melanin production (tanning) and have other effects via melanocortin receptors. Melanotan I and II are research peptides.

Also known as: MT-1, MT-2, Melanotan II

Ibutamoren, a non-peptide growth hormone secretagogue that mimics ghrelin. Taken orally, it stimulates GH and IGF-1 release.

Also known as: Ibutamoren

The mass of a molecule, typically expressed in Daltons (Da). Calculated by summing the atomic masses of all constituent atoms.

Also known as: MW

Mitochondrial Open Reading Frame of the 12S rRNA-c, a mitochondrial-derived peptide researched for metabolic regulation and exercise mimetic effects.

The end of a peptide chain with a free amino group (-NH₂). Peptide sequences are conventionally written from N-terminus to C-terminus.

Also known as: Amino Terminus, NH2 Terminus

A peptide that functions as a neurotransmitter or neuromodulator in the nervous system. Examples include endorphins, oxytocin, and substance P.

The brain's ability to reorganize itself by forming new neural connections. Some peptides like Semax may enhance neuroplasticity.

A peptide containing a small number of amino acids, typically 2-20 residues.

Taking a substance by mouth. Most peptides have poor oral bioavailability due to digestive enzyme breakdown, though some (like BPC-157) may have oral activity.

The attachment of polyethylene glycol (PEG) chains to peptides or proteins. PEGylation increases half-life, reduces immunogenicity, and improves solubility.

A chain of amino acids linked by peptide bonds. Generally refers to chains of 2-50 amino acids; longer chains are typically called proteins.

The covalent amide bond (-CO-NH-) linking amino acids in peptides and proteins. Formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another.

The study of how substances are absorbed, distributed, metabolized, and eliminated by the body (ADME). Critical for understanding peptide dosing.

Also known as: PK

The addition of a phosphate group to a molecule, typically by kinase enzymes. A key regulatory mechanism for peptides and proteins.

A peptide containing many amino acids, typically 20-50 residues. Often used interchangeably with 'protein' for longer chains.

Chemical modifications to peptides or proteins after synthesis. Includes phosphorylation, glycosylation, acetylation, methylation, and many others.

Also known as: PTM

The linear sequence of amino acids in a peptide or protein, written from N-terminus to C-terminus.

An enzyme that cleaves peptide bonds. Also called peptidase or proteinase. Proteases limit peptide half-life in the body.

Also known as: Peptidase, Proteinase

A protein that receives and responds to signals (ligands). Peptide receptors include GPCRs, receptor tyrosine kinases, and ion channels.

The process of dissolving lyophilized (freeze-dried) peptide in a suitable solvent (typically bacteriostatic water) for use.

Local folding patterns in peptides and proteins, including alpha helices, beta sheets, and turns, stabilized by hydrogen bonds.

A synthetic peptide derived from tuftsin with anxiolytic and nootropic properties. Developed in Russia, administered intranasally.

The order of amino acids in a peptide, conventionally written from N-terminus (left) to C-terminus (right) using single-letter or three-letter amino acid codes.

Solid-Phase Peptide Synthesis, the standard method for synthesizing peptides where the growing chain is attached to an insoluble resin support.

Also known as: Solid-Phase Peptide Synthesis

Administration of a substance under the skin. The most common injection route for peptides, using a short needle at a 45-90 degree angle.

Also known as: SubQ, SC

A synthetic GHRH analog FDA-approved for reducing visceral fat in HIV patients. Stimulates natural growth hormone release.

A naturally occurring thymic peptide that modulates immune function. Researched for immune support and approved in some countries for hepatitis B.

Also known as: Ta1

A peptide consisting of exactly three amino acids joined by two peptide bonds.

A standard insulin syringe concentration where 100 units equals 1 milliliter. Used to measure peptide doses: 10 units = 0.1 mL.

A molecule with both positive and negative charges that result in a net neutral charge. Amino acids exist as zwitterions at physiological pH.