Peptide ends matter: acetylation and amidation in a custom order

You have the amino-acid sequence ready. Is that enough for a peptide quote? Not always. The two ends of the chain can have different chemical groups, even when every amino acid in the middle stays the same. A supplier needs to know which version you want.

Think of the ends as part of the design

The beginning is called the N-terminus; the other end is the C-terminus. In Bachem’s notation, H- indicates a free amino end, Ac- indicates an acetylated end, -OH indicates the unmodified acid end and -NH2 indicates an amide end. These symbols carry information that a short sequence alone may leave out. [1]

One short sequence, four possible descriptions

Here is an invented ordering example using Ala–Gly–Lys. If the only choices are a free or acetylated N-end and an acid or amide C-end, there are 2 × 2 = 4 combinations. H-Ala-Gly-Lys-OH, Ac-Ala-Gly-Lys-OH, H-Ala-Gly-Lys-NH2 and Ac-Ala-Gly-Lys-NH2 are therefore four different specifications. This count does not say they behave alike or are all suitable for your work.

Acetylation is not a quality upgrade

A modified end changes the molecule. It is not simply a more premium version of the same material. If you are following a paper, copy its full structure and terminal notation. If the method is unclear, resolve that question before ordering. Do not choose a modification only because it sounds more stable.

Check the calculator as well as the quote

A molecular-weight calculation must describe the final molecule, including its ends. A calculator set to free termini can give a different result from one set to acetylation and amidation. Keep those settings with the calculated value so that you can check them against the supplier’s specification.

What to include in your enquiry

Send the sequence from N to C, mark both terminal groups, and list any side-chain changes separately. If you need two versions for comparison, give them separate identifiers and ask for separate prices. NHD’s custom synthesis enquiry is a starting point; the requested chemistry and analytical records still need confirmation.

Useful links

• Custom peptide synthesis
• Thymosin alpha-1 product family
• Send a sequence with terminal groups

For laboratory research, development and manufacturing only. Not for human or veterinary use.

Sources and examples

• Bachem: peptide notation and terminal modifications

Reference records explain the topic; they do not establish NHD stock, a supplied lot’s results or clinical suitability. Examples explicitly labeled as hypothetical are calculations, not test data.

Editorial source check: Codex AI editorial · 2026-10-03