Researcher resources

Peptide research glossary.

Definitions for the terms researchers encounter most often when working with research-grade peptides. From technique terminology (HPLC, LAL, lyophilized) to mechanism vocabulary (BDNF, AMPK, sirtuin, NF-kB) to compound classes (incretin, GHRP, melanocortin).

A

Acylation

A chemical modification adding a fatty acid chain to a peptide. Used in pharmaceutical peptides like semaglutide and Retatrutide to extend plasma half-life by promoting reversible binding to serum albumin and slowing proteolytic clearance.

Alpha-MSH

Alpha-melanocyte-stimulating hormone, a 13-amino-acid peptide hormone that activates melanocortin receptors. Its synthetic analogues include MT-1 (afamelanotide) and MT-2 (Melanotan II).

AMPK

AMP-activated protein kinase. The master cellular energy sensor that activates when cellular energy is low, triggering catabolic processes (fatty acid oxidation, glucose uptake) and inhibiting anabolic processes. Activated by MOTS-c independently of cellular AMP:ATP ratio.

B

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol as a preservative. The standard solvent for reconstituting lyophilized peptides because the benzyl alcohol prevents microbial growth across the typical 28-day working window. See the bacteriostatic water research guide.

Batch lot

A unique identifier assigned to a specific manufactured batch of a compound. Used to trace the batch’s Certificate of Analysis and quality testing data. Every Aeternum vial is marked with its batch lot number, traceable in the public COA library.

BDNF

Brain-derived neurotrophic factor. A neurotrophin that supports neuron survival, synaptic plasticity, and learning. Upregulated in the hippocampus and prefrontal cortex by Semax administration.

Benzyl alcohol

An aromatic alcohol (C6H5CH2OH) used at 0.9% concentration in bacteriostatic water as a bacteriostatic preservative. Disrupts bacterial membrane function without significant pharmacological effect at the concentration used.

C

Certificate of Analysis (COA)

A document generated by a third-party laboratory that documents the quality testing results for a specific batch lot. For peptides, the standard tests are mass spectrometry identity confirmation, HPLC purity, and LAL endotoxin screening. See the COA explainer.

Cyclic peptide

A peptide where the chain is closed into a ring through an amide bond between two amino acid residues. The cyclization confers metabolic stability against proteolytic degradation. Examples include MT-2 (Melanotan II) and Ipamorelin.

D

DAC

Drug Affinity Complex. A modification on CJC-1295 (the ‘with DAC’ variant) that binds the peptide to serum albumin, extending plasma half-life from 30 minutes to 7-10 days. The ‘No DAC’ variant lacks this modification.

E

Endotoxin

Lipopolysaccharide molecules released from the cell walls of gram-negative bacteria. Can produce inflammatory responses in research models even at picogram-per-milliliter concentrations. Detected by the LAL endotoxin assay.

EU/mg

Endotoxin units per milligram. The unit used to express endotoxin concentration in peptide samples. Research-grade peptides typically test below 1 EU/mg; ultra-low endotoxin material is below 0.1 EU/mg.

F

Freeze-thaw cycle

One complete cycle of freezing and then thawing a sample. Each cycle damages peptide structure through ice crystal formation that disrupts intramolecular hydrogen bonding. Repeated freeze-thaw cycles produce cumulative activity loss.

G

GHK-Cu

The copper-bound form of the tripeptide glycyl-histidyl-lysine. Modulates expression of more than 4,000 human genes toward profiles characteristic of younger tissue. See the GHK-Cu research guide.

GHRH

Growth-hormone-releasing hormone. A 44-amino-acid hypothalamic peptide that triggers growth hormone release from pituitary somatotropes. Synthetic analogues include Tesamorelin and CJC-1295.

GHRP

Growth-hormone-releasing peptide. A class of compounds that activate the ghrelin receptor on pituitary somatotropes, triggering GH release through a pathway parallel to GHRH. Examples: Ipamorelin, GHRP-2, GHRP-6, hexarelin.

GIP

Glucose-dependent insulinotropic polypeptide. An incretin hormone that enhances insulin secretion and modulates adipose tissue function. Activated by tirzepatide (GLP-1/GIP dual agonist) and Retatrutide (triple agonist).

GLP-1

Glucagon-like peptide-1. An incretin hormone that drives glucose-dependent insulin secretion, slows gastric emptying, and reduces appetite signaling at the hypothalamus. Activated by semaglutide (monoagonist), tirzepatide (with GIP), and Retatrutide (triple agonist).

Glutathione (GSH)

The most abundant intracellular antioxidant in mammalian cells. A tripeptide of glutamate, cysteine, and glycine. The substrate for glutathione peroxidase, glutathione S-transferase, and the cellular redox cycling system. See the Glutathione research guide.

H

HPLC

High-performance liquid chromatography. The standard analytical method for measuring peptide purity. Reverse-phase HPLC separates compounds based on hydrophobicity; the area under each peak in the chromatogram is proportional to the amount of that component.

I

Incretin

A class of gastrointestinal hormones (including GLP-1 and GIP) that enhance insulin secretion in response to food intake. Incretin-mimetic drugs (semaglutide, tirzepatide, Retatrutide) leverage this mechanism for metabolic research and treatment.

Ipamorelin

A synthetic pentapeptide GHRP that selectively activates the ghrelin receptor without elevating cortisol, prolactin, or appetite. The standard selective GHRP for research, commonly combined with CJC-1295.

L

LAL assay

Limulus amebocyte lysate assay. The standard method for detecting bacterial endotoxin contamination in peptide samples. Highly sensitive — detects endotoxin at the 0.005 EU/mL level.

Lyophilized

Freeze-dried into a stable powder form. Lyophilization removes water under vacuum at low temperature, producing a long-term-stable solid. Most research peptides ship as lyophilized vials that require reconstitution before use.

M

Mass spectrometry

An analytical method that measures the molecular weight of compounds. Used to verify peptide identity by matching the measured mass against the theoretical mass of the labeled sequence. Common variants for peptides: MALDI-TOF and ESI-MS.

MC1R / MC4R

Melanocortin receptors. MC1R is on melanocytes and primarily mediates pigmentation. MC4R is in the hypothalamus and mediates appetite, sexual function, and energy regulation. MT-1 selectively activates MC1R; MT-2 activates all melanocortin receptors.

Melanocortin

A family of peptide hormones derived from pro-opiomelanocortin (POMC) that activate the melanocortin receptors. Includes alpha-MSH, ACTH fragments, and synthetic analogues like Melanotan.

MOTS-c

Mitochondrial-derived peptide encoded in the 12S rRNA gene. Activates AMPK and improves insulin sensitivity. One of the first identified mitochondrial-derived peptides with systemic metabolic effects. See the MOTS-c research guide.

N

NAD+

Nicotinamide adenine dinucleotide. A coenzyme central to cellular energy metabolism, sirtuin enzyme activity, and PARP-mediated DNA repair. Levels decline with age in mammalian tissues. See the NAD+ research guide.

NF-kB

A transcription factor that is the master regulator of inflammatory gene expression. Inhibited by KPV and TB-500 in their anti-inflammatory mechanisms.

NMN / NR

Nicotinamide mononucleotide and nicotinamide riboside. Orally bioavailable NAD+ precursors that the cell converts to NAD+ in situ. Used as oral alternatives to direct NAD+ administration.

P

PARP

Poly(ADP-ribose) polymerase. A family of enzymes that mark sites of DNA damage for repair, consuming NAD+ in their catalytic cycle. PARP activity links cellular NAD+ availability to DNA repair capacity.

Pentadecapeptide

A peptide composed of fifteen amino acids. The structural class of BPC-157 (sequence GEPPPGKPADDAGLV).

Plasma half-life

The time required for the plasma concentration of a compound to decrease by half. A key pharmacokinetic parameter that influences dosing frequency. Tesamorelin: 26 minutes. Retatrutide: 6 days. CJC-1295 No DAC: 30 minutes.

Pulsatile release

A pattern of hormone release in discrete bursts rather than continuous elevation. Endogenous GH release follows a pulsatile pattern, which is why short-half-life GHRH analogues (Tesamorelin, CJC-1295 No DAC) are preferred for research that aims to mimic natural physiology.

R

Reconstitution

The process of dissolving a lyophilized peptide in a sterile solvent (typically bacteriostatic water) to produce a working solution. See the reconstitution master guide.

S

Sirtuin

A family of NAD+-dependent enzymes that remove acetyl groups from histone and non-histone proteins, regulating gene expression and metabolic state. Central to longevity research. Activity is rate-limited by cellular NAD+ availability.

Sterile water

Sterilized water without preservative. Suitable only for single-use applications because opened vials are vulnerable to microbial contamination. Different from bacteriostatic water, which contains a preservative.

Subcutaneous

Administered into the layer of fat just beneath the skin. The standard administration route for most research peptides because of consistent absorption and ease of self-administration in research protocols.

T

TB-500

Synthetic peptide based on the active LKKTETQ region of thymosin beta-4. Acts through actin sequestration and cell migration. See the TB-500 research guide.

Tesamorelin

Stabilized GHRH analogue developed by Theratechnologies. FDA-approved (2010) for HIV-associated lipodystrophy. The most clinically validated GHRH analogue. See the Tesamorelin research guide.

Thymosin beta-4

A 43-amino-acid actin-binding protein found in nearly every mammalian cell type. The principal actin-sequestering molecule in mammalian cells. The synthetic active fragment is TB-500.

V

VEGF

Vascular endothelial growth factor. A signaling protein that drives angiogenesis (formation of new blood vessels). Upregulated by BPC-157, contributing to its vascular and tissue-repair effects.