Molecular and biochemical characterization of an Arabidopsis thaliana arogenate dehydrogenase with two highly similar and active protein domains.

The present study reports the first molecular characterization of a plant arogenate dehydrogenase, the enzyme that catalyses the transformation of arogenate into tyrosine. The structure of the Arabidopsis thaliana tyrA gene is very peculiar since it encodes two highly similar, and putatively active, protein domains. PCR analyses confirmed the existence of a transcript encoding the two protein domains. The complete coding sequence and sequences corresponding to the two separate domains were independently cloned into Escherichia coli mutant AT 2471 lacking prephenate dehydrogenase activity. Our results revealed that the three recombinant enzymes are active. They all exhibit a high specificity toward arogenate and NADP, and have very similar kinetic properties.