You can delete a custom modification only if the modification is not currently used in any sequences loaded to the Sequence Manager.

Otherwise, if you try to delete a custom modification associated with a sequence in the Sequence Manager, an error message box appears. You must first modify the affected sequences to remove the modification before deleting the modification from the Modification Editor.

You cannot delete default modifications.


  1. In the Protein Sequence Editor, select the title bar for the Modification Editor.
  2. The Modification Editor pane opens, displaying all of the N-terminal, C-terminal, and side chain modifications available.
  3. In the modification lists on the left side, select the custom modification (in purple) that you want to delete.
  4. Select Delete in the N-Terminal, C-Terminal, or Side Chain area, as appropriate.