{"id":3025,"date":"2026-10-03T16:07:48","date_gmt":"2026-10-03T16:07:48","guid":{"rendered":"https:\/\/nhdbio.com\/?p=3025"},"modified":"2026-10-03T16:07:48","modified_gmt":"2026-10-03T16:07:48","slug":"ss31-calculateur-de-sequence-dacides-amines-non-standard","status":"publish","type":"post","link":"https:\/\/nhdbio.com\/fr\/ss31-nonstandard-amino-acids-sequence-calculator\/","title":{"rendered":"SS-31 : pourquoi quatre lettres ne suffisent pas pour calculer la masse mol\u00e9culaire"},"content":{"rendered":"

A peptide can be short and still need a detailed structural description. SS-31 is a useful example: counting four residues does not tell a calculator everything it needs to know. A nonstandard residue and the terminal group matter too.<\/p>\n

Start with the complete structure<\/h2>\n

PubChem lists the sequence description H-D-Arg-Tyr(2,6-diMe)-Lys-Phe-NH2 for compound 11764719. The modified tyrosine is often abbreviated Dmt. Here, Dmt means 2,6-dimethyltyrosine; it is not ordinary tyrosine. The D-Arg notation and the amide end also belong to the specification. [1]<\/p>\n

Check what the calculator can represent<\/h2>\n

Typing an ordinary four-letter amino-acid string cannot fully describe that structure. A suitable calculation needs to account for the nonstandard residue, terminal amidation and residue configuration. Do not assume that an unfamiliar letter or a note beside the input will change the calculation. Check the tool\u2019s supported notation first.<\/p>\n

Use reference numbers with their meaning attached<\/h2>\n

For the neutral structure in that PubChem record, the molecular formula is C32H49N9O5 and the computed molecular weight is 639.8 g\/mol. These are reference structure values, not the amount of peptide in a supplied vial. A counterion, water or a different supplied form can change the meaning of a powder-based calculation. [1]<\/p>\n

What to send with an enquiry<\/h2>\n

Send the full structure description rather than a short name alone. Ask which molecular form is proposed, which mass value is used and what identity evidence could be provided. The NHD SS-31 family page is a starting point for a research-material enquiry; it does not establish a particular lot\u2019s identity or quantity.<\/p>\n

Useful links<\/h2>\n