Acetic Anhydride Modification of Proteins

Anhydrides are usually used to modify primary amines on proteins. The protein is usually dialyzed into a buffer at pH > 7.0 (Not Tris or an other amine containing buffer) and then treated at 4 degrees in ten molar excess for an hour or two. As shown below a stabile amide forms on the protein's amines.

Acetic Anhydride Reaction
Figure 1: Reaction of acetic anhydride with primary amines