Peptide nomenclature and how to read a product name

Three naming systems in parallel

Research peptides usually carry three names at once: a systematic chemical description, a development code assigned by whoever first synthesised the molecule, and sometimes a non-proprietary generic name. BPC-157, for instance, is a development code; the systematic description is a fifteen-residue partial sequence of body protection compound.

Development codes follow no universal convention. GHRP-2 and GHRP-6 are numbered by order within a series; TB-500 references thymosin beta but is not the full protein; CJC-1295 is a company internal designation. The code alone tells you very little, which is why the sequence and mass on the certificate of analysis are the authoritative identifiers.

Fragment notation

Parenthetical ranges indicate which residues of a parent molecule are present. GHRH(1-29) is the first twenty-nine residues of growth hormone-releasing hormone. hGH(176-191) is an internal fragment of human growth hormone. When a fragment is described as retaining full activity, it means the receptor-binding determinants happen to lie within that range.

Suffixes that change the molecule

A suffix frequently marks a genuinely different compound rather than a variation in presentation. DAC denotes a drug affinity complex — a covalent albumin-binding linker that extends half-life from minutes to days. Modified in a name usually signals amino-acid substitutions made for protease resistance. PEG- indicates polyethylene glycol conjugation. LR3 on IGF-1 denotes both an N-terminal extension and a position-3 substitution.

The practical rule: if a suffix changes the molecular formula, it is a separate compound and deserves a separate specification, certificate and product record. If it changes only the quantity in the vial, it is a strength variant of the same compound.

Salt form and net peptide content

Synthetic peptides are usually isolated as trifluoroacetate or acetate salts, and the counter-ion contributes mass. A vial labelled 5 mg may therefore contain somewhat less than 5 mg of peptide by net content. Certificates that report net peptide content alongside gross weight remove this ambiguity, which matters whenever molar concentration is being calculated.

Decoding the suffixes and modifiers on a label

Most confusion in peptide naming comes from modifiers appended to a parent sequence. A trailing 'DAC' on CJC-1295 denotes a drug affinity complex — a maleimide group that covalently binds serum albumin and extends circulating residence time enormously relative to the unmodified peptide. 'No DAC' therefore describes a fundamentally different exposure profile using the same core sequence, which is why the two are treated as distinct compounds rather than as formats of one.

Terminal modifications are the second common source. 'Ac-' at the front indicates N-terminal acetylation, which caps the free amine and blocks aminopeptidase attack. '-NH2' at the end indicates C-terminal amidation, which removes the terminal negative charge and, for many receptor-binding peptides, is required for activity at all. A sequence supplied as a free acid where the literature used the amide is not the same molecule pharmacologically, and certificates should state which form was made.

Numeric fragments describe which residues of a parent protein the sequence spans. AOD-9604 corresponds to the 176–191 fragment of human growth hormone with an added tyrosine; Thymosin beta-4 fragments are named the same way. When a paper cites a fragment, matching the residue range on the certificate is the only reliable way to confirm you are working with the same material.

Salt form, net peptide content and why they change your numbers

Synthetic peptides are almost always isolated as trifluoroacetate salts because TFA is used in the final purification. The counter-ion is not inert mass to be ignored: for a basic, arginine-rich sequence, TFA can account for ten to twenty percent of vial weight. A vial labelled 10 mg of a TFA salt may contain around 8.5 mg of the peptide itself.

This is why complete certificates distinguish gross weight from net peptide content, the latter typically measured by amino acid analysis or nitrogen determination. Quantitative work — anything reporting a concentration, an EC50 or a dose-response — should be calculated from net peptide content, not from the number printed on the label.

Acetate salt forms exist and are preferred where TFA would interfere, since residual trifluoroacetate is cytotoxic to some cell lines at concentrations well below those at which it affects biochemical assays. If a cell-based readout behaves oddly at high peptide concentrations, residual counter-ion is a standard first suspect.