[diablo]

Hi folks,

i've acetylated a test peptide (which got no lysine, so only the N-terminus)  with acetic anhydride + glacial acetic acid and it worked well. Now i'll try to acetylate a peptide mix ( tryptic digest of a protein) and i wonder if anyone of you know under which condition i would get the best results ?

Should i maybe acetylate @ high pH ? ( I've read that Lysine side-chain N-terimuns reacts best under alkaline conditions...)
Anyone of you got ideas ?

Thx in advance.

regards
Diablo

[Yggdrasil]

Do you want to acetylate all free amines or just the N-termini?

[diablo]

Hi, actually i want to cover all the lysines... but if N-termini gets acetylated it wouldn't bother...

greets
Diablo

[Yggdrasil]

The pKa of the lysine side chain is about 10.  Since the protonated amine is not a good nucleophile, you would need fairly basic conditions to acetylate the lysines.  This problem is confounded by the fact that the acetylation produces acid as a byproduct.

[AWK]

Esterify lysine before acetylation

[diablo]

thx for your answers guys !


@ yggdrasil: what problems could occur with the acid byproduct?

@AWK: esterify Lysine ?? ( lysine got no OH-group ?)


greets diabloo

[AWK]

Carboxyl groups forms ester!

[Yggdrasil]

If you need to perform the acetylation under basic conditions, the production of acid will neutralize the basic conditions as the reaction proceeds.  Therefore, you need some way to buffer the solution at high pH.

After a quick google search (first hit when searching for "peptide acetylation"), I found this, which may be helpful to you:

http://www.ionsource.com/Card/acetylation/mono0003.htm

[diablo]

ok, both big thx for your help !