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Molecular Weight
Purity
Storage
Appearance
Solubility
01
GHRP-6 (growth hormone-releasing peptide-6) is a synthetic six-residue peptide and one of the first small peptides shown to stimulate growth hormone release through what is now known as the ghrelin receptor (GHS-R1a). Its sequence is His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂.
Work with GHRP-6 helped define the growth hormone secretagogue pathway years before the receptor was cloned and ghrelin was identified as its natural ligand. It remains a well-documented reference agonist, and its two tryptophan residues give it strong natural fluorescence. It is supplied as a lyophilized reference material for in vitro receptor studies, fluorescence-based methods and structure–activity comparisons across the GHRP family.
02
GHRP-6 is built around two tryptophan residues of opposite configuration, flanked by histidine and an alternating D/L pattern.
His, position 1
The N-terminal histidine has an imidazole side chain with a pKa near 6, so its charge changes across the pH range used in chromatography and MS.
D-Trp, position 2
A D-configured tryptophan that early structure–activity studies identified as important for agonist activity.
Trp, position 4
A second, L-configured tryptophan. Together the two indole rings give unusually strong UV absorbance and fluorescence for a peptide this size.
D-Phe, position 5
A D-configured aromatic residue that continues the alternating chirality pattern shared across the GHRP series.
Lys-NH₂, position 6
A positively charged, amidated C-terminus that resists carboxypeptidases.
Compared with GHRP-2, GHRP-6 has histidine instead of D-Ala at the N-terminus and D-Trp instead of D-2-Nal at position 2.
03
GHRP-6 is used as a long-established reference agonist in ghrelin-receptor research.
Historical role
Studies with GHRP-6 and related peptides characterised a growth hormone release pathway distinct from GHRH. The receptor itself was later cloned using a non-peptide secretagogue, and ghrelin was subsequently identified as its endogenous ligand.
Receptor binding and signalling
Competition binding with radiolabelled ghrelin and Gq-linked readouts, such as intracellular calcium and inositol phosphate, are used to rank GHRP-6 against GHRP-2, Ipamorelin and ghrelin.
Additional binding site
Beyond GHS-R1a, GHRP-6 has been reported to bind the scavenger receptor CD36, which is one reason it is regarded as less selective than later compounds such as Ipamorelin.
All research context described here refers to controlled in vitro and preclinical experimental systems.
04
Reference agonist
A well-documented comparator for normalising results between GHS-R1a assays and laboratories.
Fluorescence methods
Its two tryptophans give strong intrinsic fluorescence, making it a convenient calibrant for fluorimetric peptide detection.
Photostability studies
With two light-sensitive tryptophans, it is a sensitive indicator when validating light-protected storage and handling.
Structure–activity comparisons
Run alongside GHRP-2 and Ipamorelin to relate differences in sequence to differences in potency and selectivity.
05
Storage
Store the lyophilized powder at −20 °C, sealed, desiccated and protected from light. Let the vial reach room temperature before opening.
Light sensitivity
Both tryptophans can photo-oxidise, forming kynurenine-type products. Use amber or foil-wrapped containers and handle under subdued light.
Histidine oxidation
Under strongly oxidising conditions, the N-terminal histidine can oxidise (+16 Da). Avoid oxidising reagents and prolonged air exposure in solution.
Reconstitution
Soluble in water or dilute acetic acid thanks to its histidine and lysine residues. DMSO stocks diluted into buffer are also common for cell-based assays.
Labware
Use low-binding polypropylene tubes and prepare solutions fresh where possible.
06
Its aromatic residues give GHRP-6 several convenient detection options.
HPLC
Retains well on reversed-phase C18 columns. Detection at 214 nm is general, 280 nm is selective for aromatic residues, and 295 nm is more selective still for tryptophan.
Mass spectrometry
ESI-MS shows [M+H]⁺ at m/z 873.4 and [M+2H]²⁺ at m/z 437.2 (monoisotopic mass 872.44). The tryptophan immonium ion at m/z 159.1 is prominent in MS/MS.
Fluorescence
Excitation near 280 nm and emission near 340 nm allow sensitive detection; changes in emission can also indicate changes in conformation or environment.
Impurity profile
Stability-indicating methods should look for tryptophan oxidation products (kynurenine, +4 Da; N-formylkynurenine, +32 Da), histidine oxidation (+16 Da), L-epimers at positions 2 and 5, and the non-amidated free acid.
07
Both are six-residue ghrelin-receptor agonists. GHRP-6 starts with histidine and has D-Trp at position 2, whereas GHRP-2 starts with D-Ala and has D-2-naphthylalanine there. GHRP-2 is generally the more potent of the two in receptor assays.
It contains two tryptophan residues, both of which can photo-oxidise to kynurenine-type products. It should be stored in amber or opaque containers and handled under subdued light.
873.0 g/mol is the average molecular weight used for weighing and specification sheets. 872.44 is the monoisotopic mass, which is what high-resolution mass spectrometry measures ([M+H]⁺ at m/z 873.4).
Mainly tryptophan oxidation products (kynurenine at +4 Da and N-formylkynurenine at +32 Da) and histidine oxidation at +16 Da, along with L-epimers at positions 2 and 5.
No. It is supplied strictly as a reference compound for laboratory and analytical research and is not for human or animal use.
GHRP-6 Research Reference. (2026). Pure Peptides Labs Research Catalogue. Retrieved from https://purepeptideslabs.net/research-catalogue/growth-hormone-axis-research-peptides/ghrp-6/
Materials listed on this platform are supported by independent testing and published documentation for laboratory research contexts.
