BIOSYNTHESIS OF L-PHENYLALANINE AND L-TYROSINE IN THE ACTINOMYCETE AMYCOLATOPSIS-METHANOLICA

Auxotrophic mutants of the actinomycete Amycolatopsis methanolica requ iring L-Phe or L-Tyr were isolated and identified as strains lacking p rephenate dehydratase (strain GH71) or arogenate dehydrogenase (strain GH70), respectively. A. methanolica thus employs single pathways only for the biosynthesis of these aromatic amino acids. Anion-exchange ch romatography of extracts revealed two peaks with Phe as well as Tyr am ino-transferase (AT) activity (Phe/Tyr ATI and Phe/Tyr ATII) and three peaks with prephenate At activity (Ppa ATI to Ppa ATIII). Phe/Tyr ATI and Ppa ATI coeluted and appear to function as the A. methanolica bra nched-chain amino acid AT. Ppa ATII probably functions as the aspartat e AT. Mutant studies showed that Phe/Tyr ATII is the dominant AT in th e L-Phe biosynthesis and in L-Tyr catabolism but not in L-Tyr biosynth esis. Biochemical studies showed that Ppa ATIII is highly specific for prephenate and provided evidence that Ppa ATIII is the dominant AT in L-Tyr biosynthesis.