Stereochemistry of the transamination reaction catalyzed by aminodeoxychorismate lyase from Escherichia coli: Close relationship between fold type and stereochemistry

Aminodeoxychorismate lyase is a pyridoxal 5'-phosphate-dependent enzyme tha t converts 4-aminodeoxychorismate to pyruvate and p-aminobenzoate, a precur sor of folic acid in bacteria The enzyme exhibits significant sequence simi larity to two aminotransferases, D-amino acid aminotransferase and branched -chain L-amino acid aminotransferase, In the present study, we have found t hat aminodeoxychorismate lyase catalyzes the transamination between D-alani ne and pyridoxal phosphate to produce pyruvate and pyridoxamine phosphate, L-Alanine and other D- and L-amino acids tested were inert as substrates of transamination. The pro-R hydrogen of C4' of pyridoxamine phosphate was st ereospecifically abstracted during the reverse half transamination from pyr idoxamine phosphate to pyruvate, Aminodeoxychorismate lyase is identical to D-amino acid aminotransferase and branched-chain L-amino acid aminotransfe rase in the stereospecificity of the hydrogen abstraction, and differs from all other pyridoxal enzymes that catalyze pro-S hydrogen transfer, Aminode oxychorismate lyase is the first example of a lyase that catalyzes pro-R-sp ecific hydrogen abstraction. The result is consistent with recent X-ray cry stallographic findings showing that the topological relationships between t he cofactor and the catalytic residue for hydrogen abstraction are conserve d among aminodeoxychorismate lyase, D-amino acid aminotransferase and branc hed-chain L-amino acid aminotransferase [Nakai, T, Mizutani, H,, Miyahara, I., Hirotsu, K., Takeda, S., Jhee, K-H., Yoshimura, T., and Esaki, N, (2000 ) J. Biochem. 128, 29-28].