The regulation of aromatic amino acid biosynthesis in amino acid liberating mutant strains of Anabaena variabilis

Mutant strains of Anabaena variabilis which are resistant to the tryptophan analogue, 6-fluorotryptophan, liberated a wide range of amino acids although none liberated tryptophan in detectable quantities. Four strains (FT-7, FT-8, FT-9, FT-10) produced predominantly alanine together with small amounts of phenylalamine and tyrosine, strain FT-2 liberated mainly phenylalanine and tyrosine and strain FT-6 liberated mainly glutamate, NH₄⁺and several unidentified ninhydrin-positive compounds. Two forms of 3-deoxy-D-arbinoheptulosonate 7-phosphate (DAHP) synthase were identified in the parent strain, a tyrosine-sensitive form and a phenylalanine-sensitive form. In strains FT-2 and FT-6 the phenylalanine-sensitive enzyme was not detected and in strain FT-7 it was apparently deregulated with respect to inhibition by phenylalanine. No deregulation of anthranilate synthase was observed but mutant strains were found to have higher specific activities of this enzyme than the parent strain.Abbreviations chla chlorophyll a - 6-FT 6-fluorotryptophan - DAHP 3-deoxy-D-arabinoheptulosonate 7-phosphate - PEP phosphoenolpyruvate