Kisspeptin-10: Family Numbering, the Terminal Amide, and Three Degradation Routes

Kisspeptin-10 belongs to a family whose members are named by length, which is a more helpful convention than most and still manages to cause confusion. Kisspeptin-54, kisspeptin-14, kisspeptin-13 and kisspeptin-10 are not four unrelated compounds; they are four fragments of one parent, and they all end in the same ten residues. Knowing that tells you which of them a certificate can be compared against and which it cannot. This article covers the identity, the family structure, and three degradation pathways that this particular sequence is unusually exposed to.

The decapeptide, written out

The numbering is a length, and the C-terminus is shared

The parent is a 54-residue peptide, historically also called metastin, which is where the older listings under that name come from. The shorter members of the family are C-terminal fragments of it. Kisspeptin-10 is the final ten residues, and kisspeptin-13 and kisspeptin-14 are the same ten residues with three or four more on the front.

Two consequences follow. First, the compounds are not interchangeable and their masses are far apart, so no mass measurement will confuse them; the risk is in the labelling rather than the analysis. Second, and less obviously, the shared C-terminus means the longer forms can degrade toward the shorter ones. A kisspeptin-14 preparation with a peak matching kisspeptin-10 is showing a plausible related species, not a random contaminant. For a kisspeptin-10 preparation the corresponding concern runs the other way: the impurities of interest are truncations shorter than ten residues.

The amide is not a formality

The sequence ends Arg-Phe-NH2. That terminal amide, on an arginine-phenylalanine pair, is the defining motif of the RFamide peptide family, and it is a structural feature rather than a notational one. The free acid version, ending in Arg-Phe-OH, is a different molecule roughly one mass unit heavier.

This is the same problem discussed for the melanocortin group in PT-141, bremelanotide and Melanotan II, and it has the same implications here. Incomplete amidation during synthesis produces the free acid as a related impurity, the two sit about one unit apart on a molecule of 1302, and a mass reported to the nearest few units does not separate them. When a certificate resolves a target peak from a peak one unit away, that is a meaningful result. When it reports a rounded mass and a purity number, it has told you less than it appears to.

Three degradation pathways this sequence invites

Kisspeptin-10 contains, in ten residues, three of the residues most often implicated in peptide degradation. That is unusual density for such a short sequence and it is worth knowing before interpreting a chromatogram.

Tryptophan, at position 3. Tryptophan oxidizes, and its oxidation products sit 16 and 32 units above the parent. A peak near 1318 on a kisspeptin-10 preparation is the expected oxidation species. Tryptophan is also photosensitive, which is a reason vials are kept out of light rather than an abstract precaution.

Asparagine, at positions 2 and 4. Asparagine deamidates to aspartate, adding roughly one unit, usually via a cyclic intermediate that can also produce a rearranged isomer of the same mass. Two asparagines means two sites at which this can occur. The one-unit shift lands in the same region as the free-acid question above, which is precisely why coarse mass data is unhelpful for this compound: several distinct outcomes cluster within a couple of units of the target, and only a method with adequate resolution separates them.

Serine, at position 5, and the general point. Serine and the adjacent residues are where chain cleavage is most likely under thermal or pH stress. The practical upshot of all three pathways is the same: a lyophilized powder in a sealed vial, kept cold and dark, is in a different state from a reconstituted solution left at room temperature, and the certificate describes the former.

Species variants

Kisspeptin sequences are not identical across species, and kisspeptin-10 preparations exist for more than one. A listing that does not state which sequence it supplies has left the identity underspecified, and a certificate whose reference sequence differs from your expectation may be documenting a different species variant rather than a defective batch. The sequence and CAS number above are the human form, and they are the fields to reconcile against before treating a difference as a quality problem.

What a certificate here does and does not report

Batch documents we have published sit on the certificates of analysis page, each tied to a single batch and matched to a vial by cap colour and crimp colour. Not every product and not every batch has a published certificate. Batches that we do test go through HPLC as well as purity testing, and the purity guarantee page holds the commitments and the explicit non-claims. For this compound the limits of a purity figure are worth spelling out. It reports the proportion of peptide material that is the target sequence under the method used, and it does not on its own report amidation status, oxidation state, or which species variant the material was made to.

Availability in Canada

Kisspeptin-10 5mg is stocked in Canada in a 5 mg presentation, under neuropeptides alongside Selank, Semax and DSIP, each of which we have covered separately. Current pricing is on the Canadian price index.

Reading the numbers correctly

Kisspeptin-10 is the C-terminal decapeptide of a 54-residue parent, YNWNSFGLRF-NH2, 1302.4 g/mol, CAS 374675-21-5. The family numbering is a length and the members share a C-terminus. The terminal amide is structural, and the free acid sits one unit away as the characteristic synthesis-related impurity. Tryptophan oxidation adds 16, asparagine deamidation adds about one, and several distinct species therefore cluster close to the target mass, which is why resolution matters more here than the compound size suggests. Confirm the species variant before treating a sequence difference as an error.

All compounds referenced here are supplied by ExoLabz for laboratory research use only. They are not for human or veterinary use, are not authorised by Health Canada as a drug or natural health product, and nothing on this page is guidance on preparation, administration or use.