Transamination catalyzed by aminotransferase occurs in two stages. In the first step, the α amino group of an amino acid is transferred to the enzyme, producing the corresponding α-keto acid and the aminated enzyme. During the second stage, the amino group is transferred to the keto acid acceptor, forming the amino acid product while regenerating the enzyme. The chirality of an amino acid is determined during transamination. For the reaction to complete, aminotransferases require participation of aldehyde containing coenzyme, pyridoxal-5-phosphate (PLP), a derivative of Pyridoxine (Vitamin B). The amino group is accommodated by conversion of this coenzyme to pyridoxamine-5-phosphate (PMP). PLP is covalently attached to the enzyme via a Schiff Base linkage formed by the condensation of its aldehyde group with the ε-amino group of an enzymatic Lys residue. The Schiff base, which is conjugated to the enzyme's pyridinium ring, is the focus of the coenzyme activity.
:The product of transamination reactions depend on the availability of α-keto acids. The products usually are either alanine, aspartate or glutamate, since their corresponding alpha-keto acids are produced through metabolism of fuels. Being a major degradative aminoacid pathway, lysine, proline and threonine are the only three amino acids that do not always undergo transamination and rather use respective dehydrogenase.
:Alternative Mechanism
:A second type of transamination reaction can be described as a nucleophilic substitution of one amine or amide anion on an amine or ammonium salt. For example, the attack of a primary amine by a primary amide anion can be used to prepare secondary amines:  
:RNH + RNH → RRNH + NH  
:Symmetric secondary amines can be prepared using Raney nickel (2RNH → RNH + NH). And finally, quaternary ammonium salts can be dealkylated using ethanolamine: 
:RN + NHCHCHOH → RN + RNHCHCHOH  
:Aminonaphthalenes also undergo transaminations.