How to read a peptide sequence.
A peptide's sequence is its name in chemistry: every catalog entry, lab report and paper writes the molecule as a string of codes with a few prefixes and suffixes. Once the conventions are clear, a line such as Ac-LKKTETQ-OH or GHRH(1-29)-NH2 reads as plainly as a formula. Here are the rules, with examples from the compounds in the research library.
N on the left, C on the right.
Sequences are always written from the N-terminus, the end with the free amino group, to the C-terminus, the end with the carboxyl group. GEPPPGKPADDAGLV, BPC-157, starts with glycine and ends with valine. N-terminus vs C-terminus explains why the two ends differ and why synthesis builds the chain backwards from the C end.
One letter or three.
Each of the twenty standard amino acids has a one-letter and a three-letter code: G or Gly for glycine, K or Lys for lysine, W or Trp for tryptophan. One-letter strings are compact, GHK; three-letter strings with hyphens are unambiguous when unusual residues appear, Gly-His-Lys. The amino acid chart lists every code with its mass, and the glossary defines the terms used below.
Ac- and -NH2.
A prefix Ac- means the N-terminal amino group carries an acetyl group, as in Ac-LKKTETQ, TB-500. A suffix -NH2 means the C-terminal carboxyl has been replaced by an amide, as in sermorelin, GHRH(1-29)-NH2; -OH, when written, means the free acid. Each cap changes the formula and mass by a fixed amount, which the calculator applies with its Ac and NH2 options.
D-, Aib, Nal, Dmt.
A D- prefix marks the mirror-image form of a residue: D-Ala at position 2 of Mod GRF 1-29 is what blocks the DPP-IV cut. In one-letter strings the D form is sometimes written in lowercase, so aDAIF... would mean D-Ala first. Aib is 2-aminoisobutyric acid, a non-standard residue that starts ipamorelin; 2-Nal is 2-naphthylalanine, in ipamorelin and GHRP-2; Dmt is 2',6'-dimethyltyrosine, the second residue of SS-31. These residues have no one-letter code, so sequences that contain them are written in three-letter form.
GHRH(1-29), hGH 177-191.
A name followed by a residue range is a fragment of a longer parent, numbered from the parent's first residue: GHRH(1-29) is the first 29 residues of the 44-residue hormone, and AOD-9604 is hGH 177-191 with an added tyrosine. Substitutions are written as the new residue and its position, so Gln8 means glutamine at position 8 of the parent numbering, whatever the fragment's own length. Peptide fragments collects the fragments in the library.
What is attached and what is mixed.
Attachments are named after the sequence: CJC-1295 with DAC carries a maleimidopropionic acid linker on a thirtieth lysine, written as Lys(MPA) or described in words. A metal complex is written with the metal after the peptide, GHK-Cu, meaning the tripeptide bound to copper(II); why GHK-Cu is blue covers that complex. A blend is two sequences in one vial and is written as two names with a plus sign, CJC-1295 + ipamorelin, never as one sequence.
Every sequence written out.
Each Helion compound page writes the full sequence in both codes with its caps and unusual residues, so the lab report's identity result can be checked against a formula rather than a trade name.
Specs and storage by compound.
Questions (7)
Which end of a peptide sequence comes first?
The N-terminus, the end with the free amino group, is written on the left; the C-terminus on the right.
What does Ac- mean in a peptide sequence?
An acetyl cap on the N-terminal amino group, as in TB-500, Ac-LKKTETQ.
What does -NH2 mean at the end of a sequence?
The C-terminus is an amide rather than a free carboxylic acid, as in sermorelin and ipamorelin.
What does D-Ala mean?
The mirror-image (D) form of alanine. Proteins use the L form; synthetic peptides use D residues to resist enzymes.
What does GHRH(1-29) mean?
Residues 1 to 29 of growth-hormone-releasing hormone, numbered from the parent's first residue; sermorelin is this fragment with an amide cap.
What is Aib?
2-aminoisobutyric acid, a non-standard residue with no one-letter code; it is the first residue of ipamorelin.
How is a blend written?
As two names joined by a plus sign, such as CJC-1295 + ipamorelin, because the vial holds two separate molecules.
Published studies (1)
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.