Arogenate (pretyrosine) is an obligatory intermediate of L-tyrosine biosynthesis: confirmation in a microbial mutant.

Wild-type Brevibacterium flavum has been shown to possess arogenate dehydrogenase activity and to lack prephenate dehydrogenase, thereby providing presumptive evidence that arogenate (previously named "pretyrosine") is an obligatory intermediate of L-tyrosine biosynthesis. A similar enzymological pattern has been discerned in extracts made from wild-type cultures of various species of cyanobacteria. Application of rigorous molecular genetic criteria in confirmation of the exclusive role of arogenate in L-tyrosine synthesis was made possible by the isolation of an auxotrophic mutant exhibiting a nutritional requirement for L-tyrosine. The mutant was found to lack activity for arogenate dehydrogenase and to accumulate substantial amounts of arogenate behind the mutant block during starvation for L-tyrosine.