IDENTIFICATION OF POSTTRANSLATIONAL MODIFIED AMINO-ACIDS

Methylated lysines (N-epsilon-mono-methylated, N-epsilon-di-methylated and N-epsilon-tri-methylated) have been identified after derivatizati on with orthophthaldialdehyde (OPA) by using pre-column and post-colum n derivatization techniques. Also the N-epsilon-acetylated lysine and N-epsilon-formylated lysine have been identified by OPA post-column de rivatization techniques but only in free form due to their instability under acidic conditions which are used for protein hydrolysis. Additi onally, all the modified amino acids mentioned above have been derivat ized with DABITC/PITC, an Edman reagent, and identified as DABTH-deriv atives on thin-layer polyamide sheets.