SEQUENCING OF PEPTIDES AND PROTEINS WITH BLOCKED N-TERMINAL AMINO-ACIDS - N-ACETYLSERINE OR N-ACETYLTHREONINE

Many proteins cannot be directly sequenced by Edman degradation because they have a blocked N-terminal residue. A method is presented for deblocking such proteins when the N-terminal residue is N-acetylserine (which occurs frequently in eukaryotic proteins) or N-acetylthreonine. The method has been applied successfully to the determination of the N-terminal amino acid sequence of human, bovine, and rat parathymosins. Prothymosin α and other blocked proteins and peptides were also readily deblocked and sequenced by this procedure. It is proposed that the mechanism of the deblocking reaction involves an acid-catalyzed N→O shift of the acetyl group followed by a β-elimination.