Identification of post-translational modified amino acids

Methylated lysines (N^sup ^-mono-methylated, N^sup ^-di-methylated and N^sup ^-tri-methylated) have been identified after derivatization with orthophthaldialdehyde (OPA) by using pre-column and post-column derivatization techniques. Also the N^sup ^-acetylated lysine and N^sup ^-formylated lysine have been identified by OPA post-column derivatization techniques but only in free form due to their instability under acidic conditions which are used for protein hydrolysis. Additionally, all the modified amino acids mentioned above have been derivatized with DABITC/PITC, an Edman reagent, and identified as DABTH-derivatives on thin-layer polyamide sheets.[PUBLICATION ABSTRACT]