The Name on the Vial Is Three Claims at Once

A research peptide name reads as noise until the conventions click into place. Brackets, number ranges, prefixes, suffixes and salt designations are each doing specific work, and almost none of it is decorative. What follows is a practical key to the notation.

Reading a sequence

Every amino acid carries two codes: three letters (Gly, Ala, Lys) and one (G, A, K). Sequences run left to right from N-terminus to C-terminus, matching the direction of biosynthesis, so the tripeptide KPV resolves as Lys-Pro-Val, which is lysine, proline, valine.

Direction is not a formality. Lys-Pro-Val and Val-Pro-Lys share a composition and are different molecules. Where a paper prints a sequence without saying which way it runs, N-to-C is the default reading.

Number ranges mean fragments

A range in parentheses marks out a contiguous slice of some longer parent sequence. ACTH(4-10) is residues 4 through 10 of adrenocorticotropic hormone. hGH(176-191) is the C-terminal fragment of human growth hormone sold as AOD-9604. GRF(1-29) is the opening 29 residues of growth hormone-releasing factor, which is the molecule normally listed as sermorelin – though the primary literature files it under the fragment notation rather than the trade name.

That gap between what the literature calls something and what a supplier calls it is a persistent obstacle when hunting for source material. A compound name that turns up almost nothing is worth re-running as a fragment notation.

Square brackets mean substitutions

Brackets ahead of a parent name enumerate what was changed. [Nle&sup4;,D-Phe&sup7;]-α-MSH unpacks as the alpha-MSH sequence carrying norleucine at position 4 and D-phenylalanine at position 7. Sawyer and colleagues introduced precisely that analog, measuring a large increase in potency along with resistance to enzymatic degradation in the frog skin melanophore bioassay (PNAS, 1980; PMID 6777774).

Two kinds of substitution account for most of what appears inside the brackets:

• D-amino acids. Residues occurring in nature are L-form, and proteases are stereospecific, so dropping the D-enantiomer into a cleavage site slows degradation. A D- prefix is always flagging this.
• Non-proteinogenic residues. Norleucine (Nle), aminoisobutyric acid (Aib), ornithine (Orn) and others sit outside the standard twenty. Aib in particular gets used to block DPP-4 cleavage in incretin analogs.

What the ends are doing

By default the C-terminus is a free carboxylic acid. An -NH₂ or -amide suffix says it has been amidated, which mirrors many native hormones and improves stability; GRF(1-29)NH₂ is that amidated form. At the other end, N-terminal acetylation, written Ac-, caps the free amine. Either change strips a charged terminus and shifts both stability and receptor interaction.

Names that encode a half-life strategy

Some of what appears in a name has nothing to do with sequence. DAC abbreviates Drug Affinity Complex: a maleimide group forming a covalent bond with cysteine-34 of serum albumin, which lengthens circulating half-life substantially. That is the whole reason “CJC-1295 with DAC” and “CJC-1295 without DAC” behave differently in pharmacokinetic terms while sharing a core sequence, the latter being essentially modified GRF(1-29). Jetté and colleagues characterized the conjugation chemistry and its effect in rats (Endocrinology, 2005; PMID 15817669).

Fatty-acid acylation reaches a comparable endpoint by a non-covalent route, hanging a lipid chain off the peptide that binds albumin reversibly.

Salt form, and the arithmetic it changes

Peptides carrying basic residues are generally isolated as salts. TFA, trifluoroacetate, is what reversed-phase purification leaves behind by default. Acetate is substituted where TFA would interfere with an assay, since TFA is cytotoxic in cell culture above a certain concentration.

The counter-ion has mass of its own. Between that and residual water, net peptide content typically lands at 70–90% of vial weight, which is exactly why a gravimetric concentration calculation needs the net-content figure rather than the weight printed on the label.

Quick reference

• [Xⁿ] – substitution at position n
• D- – D-enantiomer, for protease resistance
• (n-m) – fragment spanning residues n through m
• -NH₂ – amidated C-terminus
• Ac- – acetylated N-terminus
• DAC – albumin-binding conjugate
• TFA / acetate – salt form

Browse the research peptide catalog, or read our guide to reading a certificate of analysis.

All products referenced are supplied for laboratory research use only and are not approved for human consumption or for clinical or veterinary use.

Related listings. Fragments carried in this catalog: Sermorelin as GHRH(1-29), AOD-9604 as hGH 176-191, TB-500 as the thymosin beta-4 17-23 region, and Semax as ACTH(4-7).