Arogenate dehydrogenases may utilize NAD+ (EC 1.3.1.43), NADP+ (EC 1.3.1.78), or both (EC 1.3.1.79). NADP+-dependent enzymes usually predominate in higher plants. The enzyme from the cyanobacterium Synechocystis sp. PCC 6803 and the TyrAAT1 isoform of the plant Arabidopsis thaliana cannot use prephenate as a substrate, while the Arabidopsis isoform TyrAAT2 can use it very poorly [2,3].