Acetylation caps a free amine on a peptide with an acetyl group (CH3CO–). Most commonly it is applied at the N-terminus, where it adds 42.01 Da to the molecular mass and removes the terminal positive charge; it can also occur on lysine side chains. In catalog names it appears as the "N-Acetyl" or "Acetyl" prefix.
What acetylation does
Aminopeptidases attack peptides from a free N-terminal amine. Acetylation removes that handle, and analogs carrying it typically survive longer in plasma and tissue-homogenate stability assays than the parent sequence. It also makes the N-terminus more hydrophobic, which slightly increases retention time on reverse-phase HPLC — a useful cross-check that the modification is actually present.
Where it appears in this catalog
N-Acetyl Semax Amidate and N-Acetyl Selank Amidate combine acetylation with C-terminal amidation, giving doubly capped backbones. Argireline (acetyl hexapeptide-8) and SNAP-8 are acetylated cosmetic research peptides.
Why it matters
Acetylation is not an inert label. It changes the theoretical mass a mass spectrometry result must match, changes chromatographic behaviour, and means the acetylated and unmodified versions of a sequence are distinct research materials that should not be treated as interchangeable.