The PT-141 peptide (bremelanotide) is a synthetic cyclic heptapeptide, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, studied in vitro as a ligand of the melanocortin receptors MC1R through MC5R. This guide describes PT-141 strictly as a molecule: its structure, its ring chemistry, and how its receptor interactions are characterized in cell-based and binding assays.
What is the PT-141 peptide?
PT-141 is the common research name for bremelanotide, a seven-residue peptide analogue of the melanocortin pharmacophore found in alpha-melanocyte-stimulating hormone (alpha-MSH). It is described here only as a laboratory reference material and receptor ligand.
What is its chemical structure?
| Property | Value |
|---|---|
| Chemical name | Bremelanotide (PT-141) |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| Class | Cyclic heptapeptide (lactam-bridged) |
| Molecular formula | C50H68N14O10 |
| Molecular weight | 1025.18 g/mol |
| CAS number | 189691-06-3 |
| PubChem CID | 9941379 |
How does the cyclic structure define it?
The ring is closed by a lactam bond between the side-chain carboxyl of aspartic acid and the side-chain amine of lysine. That bridge constrains the His-D-Phe-Arg-Trp core, the short motif shared across melanocortin ligands, into a fixed conformation. Two further substitutions distinguish it from the native hormone sequence: norleucine (Nle) in place of methionine, and D-phenylalanine in place of L-phenylalanine. The N-terminus is acetylated and the C-terminus is a free acid. The ring chemistry is shared with Melanotan II, which differs only at the C-terminus (see the PT-141 vs Melanotan II comparison).
Which melanocortin receptors does it engage in vitro?
Melanocortin receptors are class A G-protein-coupled receptors (GPCRs) that couple to Gs and raise intracellular cAMP when activated. In research literature PT-141 is characterized as a non-selective agonist across the family, with notable affinity at MC3R and MC4R.
| Receptor | Signaling | Typical in vitro system |
|---|---|---|
| MC1R | Gs / cAMP | HEK293 or CHO cells expressing the human receptor |
| MC2R | Gs / cAMP; requires MRAP accessory protein; ACTH-selective | Cells co-expressing MC2R and MRAP |
| MC3R | Gs / cAMP | HEK293 or CHO stable lines |
| MC4R | Gs / cAMP | HEK293 or CHO stable lines |
| MC5R | Gs / cAMP | HEK293 or CHO stable lines |
How is PT-141 studied in vitro?
Two assay families dominate. Competition binding uses a radiolabeled reference ligand to determine Ki, and functional assays measure cAMP accumulation or a CRE-reporter readout to determine EC50 and efficacy. Running the same peptide lot across all five receptor-expressing lines gives a selectivity profile. For assay formats and controls, see GPCR binding assays in vitro and the background on the melanocortin receptor family.
Where to source PT-141 as a research material
Happy Peptides supplies PT-141 (CAS 189691-06-3, about 99% by HPLC) as a lyophilized research material with batch documentation. What to check on the certificate is covered in Sourcing PT-141 as a research material, and ways to confirm identity are in PT-141 name variants and mass-spec verification. Stock preparation is worked through in the 10 mg vial concentration guide below.
Related research guides
- PT-141 10 mg vial: stock concentration math
- The melanocortin receptor family: a research primer
- PT-141 melanocortin-receptor binding in vitro
- Melanocortin and peptide-receptor research compounds: overview
Research-use note
All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.
