This example from the aminotransferase subclass is responsible for a reversible transamination reaction in E. coli, which is dependant upon the cofactor pyridoxal-5'-phosphate (PLP).  This reaction occurs between L-branched-chain amino acids and α-keto acids.

This class of enzymes is located in both the mitochondria and cytosol of various organisms.  In humans, it is responsible for the production of urea from L-arginine in the urea cycle, as well as the production of various amino acids from α-keto acids.  In E. coli, aminotransferase enzymes are responsible for the biosynthesis of amino acids L-leucine, L-tyrosine, and L-phenylalanine. The general mechanism for this type of reaction can be found here.

The enzyme structure consists of three groups of dimers, or a trimer of dimers.  Each dimer contains one PLP molecule and two active sites (28Å apart), facing the solvent region, for conversion of L-branched-chain amino acids.  There are a total of three different protein chains consisting of 309 residues each, for a grand total of 1,236 residues.  The secondary structure of each dimer consists of an α/β configuration, or a mixture of both α-helix and β-sheet intertwined in a mixed manner, to form a β-barrel roll in each dimer. Each dimer or chain consists of 10-11 α-helices and 22 β-sheets.