The N-terminal end of a peptide normally carries a positive charge and is the point of attack for aminopeptidases, enzymes that break the chain down from its start. Acetylating it neutralises that charge and blocks that attack.
It is one of the most common modifications in nature (a large share of human proteins are acetylated at the N-terminus) and a routine tool in analogue design: it extends stability in biological media without changing the core sequence.
Acetylation adds 42 Da to the molecular weight. Like amidation at the other end, it is an identity datum: an “Ac-peptide” and the same peptide without acetylation are different molecules, and the mass analysis must reflect that.
When a supplier offers an “N-acetyl” or “amidated” variant of a well-known peptide, it is offering a different molecule. Comparing prices or results between them as if they were the same is a common mistake.
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Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).