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Research Library

Reading Peptide Identity Data

Updated: September 24, 2026

Each compound page on this site has a Chemical identity section. This guide explains what each value means and where it comes from.

Where the values come from

Every value names its source: usually PubChem, the U.S. National Library of Medicine's chemistry database, or, for proteins such as HGH and HCG, the FDA's Global Substance Registration System. Where no registry record could be cited, the value is left out rather than filled in.

CAS number

A CAS Registry Number is an identifier the Chemical Abstracts Service assigns to one specific substance. Different names for the same compound share a CAS number, while different forms of a compound, such as a salt and its free base, can each have their own.

Molecular formula and weight

The formula counts the atoms of each element in one molecule: C62H98N16O22 for BPC-157. The molecular weight is the average mass of one mole of the compound, in grams per mole. For a peptide made only of standard amino acids, both can be calculated from the sequence, and each such peptide on this site has its formula and weight recomputed from its sequence by an automated check.

One-letter and three-letter sequences

A sequence is written from the N-terminus to the C-terminus. The one-letter form GEPPPGKPADDAGLV and the three-letter form Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val describe the same 15 amino acids.

Modified peptides

Many research peptides are not plain chains, and their notation carries extra marks:

  • "Ac-" at the start means the N-terminus is acetylated, and "-NH2" at the end means the C-terminus is an amide, as in SNAP-8.
  • A "D-" prefix marks the mirror-image form of an amino acid, as in GHRP-2.
  • Nle (norleucine), Dmt (2′,6′-dimethyltyrosine) and 2-Nal (3-(2-naphthyl)alanine) are amino acids outside the standard twenty; Dmt appears in SS-31.
  • "cyclo[...]" marks a ring. MT-2 and PT-141 share the same ring and differ only at the C-terminus: an amide in MT-2, a free acid in PT-141.

Salts and complexes

Some registry entries describe a charged form. PubChem lists 5-Amino-1MQ as a cation and GHK-Cu as a copper complex cation, and the formula and weight of a supplied salt also include its counter-ion.

Identity data and testing

Registry data describes the compound. Whether a particular vial contains it is a question for that batch's report: see How to Read a Certificate of Analysis.

For laboratory research use only. Not for human or animal use. This content is educational and does not constitute medical advice.
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