Melanotan II is a cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone: Ac-Nle-Asp-His-DPhe-Arg-Trp-Lys-NH2, closed through a lactam bridge. Molecular formula C50H69N15O9, molecular weight 1024.2 g/mol.
It is a truncated and cyclised derivative of the native thirteen-residue hormone. Reducing alpha-MSH to a seven-residue ring preserved melanocortin activity while producing a far more metabolically stable molecule — a well-cited demonstration that a constrained cyclic fragment can outperform the linear sequence it came from.
Research context
MT-II is a broad melanocortin agonist, active at MC1R, MC3R, MC4R and MC5R rather than selective for any one. That breadth is the defining feature for research purposes and cuts both ways.
Published work spans melanogenesis via MC1R and central endpoints via MC4R, including appetite regulation and sexual arousal pathways. But the lack of selectivity means pigmentation effects appear in studies designed around behavioural endpoints, and vice versa — a confound that has to be controlled for rather than ignored.
Two related compounds in this catalogue exist precisely because of that. PT-141 is a metabolite of MT-II with a free carboxyl in place of the C-terminal amide, shifting selectivity toward MC4R. Melanotan I retains the linear alpha-MSH structure with a more MC1R-weighted profile. Researchers isolating a single receptor pathway generally reach for one of those instead.
For a fuller treatment of the sequence, published models and technical data, see the Melanotan II research guide.
Specification
CAS number 121062-08-6. Supplied as a white lyophilized powder, soluble in water. This batch assayed at 99.31% purity, verified by HPLC and LC-MS at ILS Lab.
Handling
Reconstitute with bacteriostatic or sterile water, introducing the diluent against the vial wall and swirling gently rather than shaking. Store lyophilized at −20°C protected from light; refrigerate at 2–8°C once reconstituted.
Ships with a batch-specific Certificate of Analysis. Cross-check the batch ID printed on your vial against the CoA before use — see the guide to reading a CoA if you are unfamiliar with the format.
Frequently asked questions about Melanotan II
What is the difference between Melanotan I and Melanotan II?
Structure and selectivity. Melanotan I is linear and thirteen residues, closely tracking native alpha-MSH, with activity weighted toward MC1R. MT-II is a cyclised seven-residue fragment active broadly across MC1R, MC3R, MC4R and MC5R. For melanogenesis work specifically, MT-I’s narrower profile makes attribution cleaner; MT-II engages multiple pathways simultaneously.
Why is MT-II considered less selective?
Because shortening and cyclising alpha-MSH preserved melanocortin activity without preserving discrimination between receptor subtypes. The molecule binds all four with meaningful potency. In practice that means a study designed around central MC4R endpoints will also see MC1R-driven pigmentation effects, and one designed around pigmentation will engage central receptors. Neither can be ignored; both have to be controlled for.
MT-II or PT-141?
PT-141 is a metabolite of MT-II — one functional group different, a free carboxyl where MT-II has an amide — and that shift weights it toward MC4R. For behavioural or central endpoints, PT-141 avoids the pigmentation confound. MT-II remains the choice where broad melanocortin engagement is the point rather than a problem.
How stable is MT-II?
Considerably more stable than native alpha-MSH, which is much of why it was developed. The lactam bridge constrains conformation and the D-phenylalanine resists peptidase cleavage. Reconstitute with bacteriostatic or sterile water, swirling gently. Store lyophilized at −20°C protected from light; refrigerate at 2–8°C once reconstituted.
Research use only. Not for human or veterinary use, not for use in diagnostic procedures, and not evaluated by the U.S. Food and Drug Administration.
