Understanding Peptide Sequences: How to Read the Letters

Amino acids are written either in three-letter code (Gly, His, Lys) or one-letter code (G, H, K). The information is identical and the choice is a matter of space: three-letter code is more readable, one-letter code fits a long sequence on one line.

BPC-157 is GEPPPGKPADDAGLV. Fifteen letters, fifteen residues: glycine, glutamate, proline, proline, proline, glycine, lysine, and so on. Sequences are read left to right from the N-terminus to the C-terminus, which is the opposite of the order solid-phase synthesis actually builds them in. That asymmetry is set out in how peptides are made.

Amino Acid Sequence

• ·A D- prefix (D-Phe, D-2-Nal). A mirror-image amino acid. Naturally occurring residues are the L-form; the D-form is the enantiomer, and proteases that evolved to cut L-form chains handle it poorly. A D-residue in a sequence is almost always a deliberate stability choice, and it is common in secretagogues.
• ·Non-standard residues (Aib, 2-Nal, Sar). Synthetic amino acids: aminoisobutyric acid, naphthylalanine, sarcosine. They appear where the twenty standard residues do not deliver the conformational or stability property the designer wanted.
• ·A -NH2 suffix. C-terminal amidation, which replaces the terminal carboxyl with an amide. Another stability modification, and one that changes the molecular weight, which is how mass spectrometry distinguishes an amidated variant from an unamidated one.
• ·An N-Acetyl prefix. Acetylation of the N-terminus. N-Acetyl Semax and Semax are different molecules with different masses and separate certificates, not two grades of one product.
• ·A metal designation (GHK-Cu). A complex of the peptide with a metal ion. The copper is not part of the chain; it is coordinated to it, and it accounts for a good deal of the compound's published activity.

The sequence fixes the theoretical molecular weight, and the molecular weight is what mass spectrometry compares the vial against. That chain of reasoning is the whole reason a published sequence is more than decoration: a listing that shows a sequence, a molecular formula and a molar mass is showing you the data you need to audit its own certificate.

A listing that shows none of them is asking for trust in place of proof. It is a small tell and a reliable one, because publishing the specifications is free and only inconvenient if they would not survive checking. Every product page in this catalogue publishes sequence, formula, molar mass, CAS number and, where the compound is indexed, a PubChem identifier.

KPV: Lys-Pro-Val. Three residues, the C-terminal fragment of alpha-MSH. A sequence this short is trivial and cheap to synthesise, which is precisely why identity testing carries all the weight here: a substitute costs almost nothing.

Epitalon: Ala-Glu-Asp-Gly, or AEDG. Four residues. Same reasoning as KPV.

Ipamorelin: Aib-His-D-2-Nal-D-Phe-Lys-NH2. Five residues carrying a non-standard residue, two D-form residues and an amidated terminus. Almost every annotation described above appears in one short sequence, and every one of them shifts the mass, which is why a synthesis that dropped any of them would still look clean on a purity chromatogram.

GHK-Cu: Gly-His-Lys plus copper. Three residues and a coordinated metal ion, the smallest sequence in the catalogue with the largest cosmetic-market shadow.

Amino Acid Sequence

Amino Acid Sequence

Amino Acid Sequence

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