N (α) Selective Acetylation of Peptides

A chemical tag at the peptide N-terminus, in combination with MS, can be useful for quantitative analysis, N-terminal peptide identification, or peptide sequencing. Here we report on the N (α) selective acetylation of a peptide using acetic anhydride, a popular reagent for the modification of amino groups, without the need for the blocking of lysine side-chain ε-amino groups, which is usually required for N (α) selective acetylation. By controlling the amount of acetic anhydride used and running the reaction at 0°C, it is possible to preferentially acetylate the α-amino group. As a typical application of the method, a tryptic digest of an N-terminally blocked protein, cytochrome c, was directly acetylated using the present method. When deuterated acetic anhydride was used as the reagent, the N-terminal blocked peptide could be easily identified as a non-labeled ion peak while the N (α)-acetyl groups of all the other peptides were deuterated.