G Aminotransferases (transaminases) must deaminate one amino acid and add an amino group to another amino acid during transamination. How do the two processes differ? The second part of the reaction (adding an amino group) is the reverse of the first (deamination). The second part of the reaction takes place at a separate amino acid residue in the active site. The coenzyme PLP must be activated by an external amino group before it can catalyze the removal of the amino group from the first amino acid. The first reaction involves the formation of a Schiff base, whereas the second does not.