An electron pair on the negatively charged oxygen atom moves back into a p
bond with the carbonyl carbon (
) as the peptide bond between that carbon and the amine nitrogen breaks (
). The positive charge on Asp25
's carboxyl carbon is neutralized by an electron pair on the negatively charged oxygen (
The peptide bond has been broken. The fragment with a new N-terminus is free to diffuse away, as is the fragment with the new C-terminus if the hydrogen bond between it and Asp125 is broken.