Reference

Glossary.

Plain-language definitions for the terms that come up across peptide research.

26 terms, organized alphabetically

26 terms

A

Accelerated approval: An FDA pathway that approves a drug for a serious condition based on early evidence, on the condition that follow-up trials confirm the benefit.
Acetylation / amidation: Chemical caps (Ac, NH₂) added to a peptide’s ends to slow its breakdown. “N-acetyl ... amidate” means both ends are capped.
Agonist: A molecule that activates a receptor, mimicking the body’s own signal. An antagonist blocks it.
Amino acids (aa): The building blocks of peptides, shown as beads in the drawings. One-letter codes: G = glycine, K = lysine, and so on. A lowercase letter means the mirror-image D-form.
Amylin: A hormone released with insulin that signals fullness through the brainstem. The target of cagrilintide and eloralintide.
Angiogenesis: The growth of new blood vessels. Helpful for healing, but also what tumors need to grow, which is why pro-healing peptides raise cancer questions.

Certificate of analysis (COA): A lab report on a batch’s identity and purity. Most useful when done by an independent lab and matched to your batch number.
Computed model: A 3D shape calculated by software from a molecule’s atoms and bonds, not measured in an experiment.
Cryo-EM: Cryo-electron microscopy. Molecules are frozen in a thin layer of ice and photographed thousands of times with an electron microscope; the images are combined into a 3D map.

Endotoxin: Fragments of bacterial cell walls that survive sterilization. Injected, they can cause fever, chills and serious inflammatory reactions.

Ghrelin mimetic (GHRP): A compound that activates the ghrelin (“hunger hormone”) receptor, which also triggers GH release. Ipamorelin is one.
GHRH: Growth-hormone-releasing hormone, the brain signal that tells the pituitary to release GH. Mimicked by sermorelin, CJC-1295 and tesamorelin.
GLP-1 / GIP: Gut hormones released after eating that raise insulin and reduce appetite. The basis of today’s weight-loss drugs.

Half-life: The time it takes for half a dose to be cleared. Minutes for many natural peptides; about a week for drugs engineered with fatty-acid chains.

IGF-1: Insulin-like growth factor 1, made in the liver in response to growth hormone. It carries out many of GH’s effects.

Lyophilized: Freeze-dried into a powder, which keeps peptides stable in storage. They must be dissolved before use, which adds its own contamination and measuring risks.

Melanocortin receptors: Five receptors (MC1R–MC5R) that control skin pigment, appetite, sexual arousal and inflammation. Targeted by the Melanotans, PT-141 and KPV.
Mitochondria: The structures inside cells that turn food into ATP, the cell’s energy currency. The target of SS-31, MOTS-c and NAD+.

NMR: Nuclear magnetic resonance. Measures molecules in solution with strong magnets and radio waves, and gives a set of likely shapes rather than one.

Peptide: A short chain of amino acids, usually under about 50. Longer chains are called proteins. Many hormones are peptides.
Phase 1 / 2 / 3: Stages of human drug testing: safety in a few people, then effectiveness in hundreds, then large confirmatory trials in thousands. Most compounds fail along the way.
Protein Data Bank (PDB): The free worldwide archive of 3D structures of proteins and other molecules measured in experiments. Each entry has a four-character code, like 7KI0.

Research use only (RUO): A label for chemicals sold for lab experiments. It lets products reach the market without the testing and manufacturing controls required for drugs.
Resolution: How sharp a structure is, measured in ångströms (Å; a ten-billionth of a meter). Smaller is sharper.

WADA: The World Anti-Doping Agency. Its S0 category bans any substance not approved for human use, which covers most of this catalog.

X-ray crystallography: Molecules are packed into a crystal and hit with X-rays; the pattern the rays make reveals where each atom sits.