Action of substituted phenylalanines on Escherichia coli

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Abstract
A synergic effect of phenylalanine and tyrosine for tryptophan was demonstrated in the case of a tryptophanless mutant of E. coli. For a phenylalanineless mutant, tyrosine, but not tryptophan, showed a sparing effect. For a tyrosineless mutant, neither tryptophan nor phenylalanine showed a sparing effect. These results are best explained by a "straight" scheme for the biogenetic relationships of the 3 aromatic amino acids. p-Aminophenyl-alanine, p-nitro-phenylalanine and m-nitrotyrosine interefere with the utilization of tyrosine in E. coli, wild type, and its mutants; m- nitrotyrosine also disturbs the synthesis of tryptophan; p-fluorophenylalanine and beta-phenylserine inhibit the conversion of phenylalanine into tyrosine. Alternative pathways were suggested which lead directly (a) from tryptophan to tyrosine, and (b) from phenylalanine to the product into which the cell normally transforms tyrosine. None of the strains studied was affected by m-nitro-, m-amino-, p-nitro- or p-amino-beta-phenylserine. However, the m-amino and m-nitro compounds counteracted the inhibition caused by p-amino- and p-fluorophenylalanine, m-nitrotyrosine and beta-phenylserine in E. coli, wild type. Tryptophan showed a much stronger sparing effect in the phenylalanineless mutant, when the latter was inhibited by p.-aminophenylalanine than when it was not; tyrosine showed a strong sparing effect on phenylalanine in the inhibited phenylalanine mutant; phenylalanine was more active than tyrosine in restoring the growth of the inhibited tyrosineless mutant of E. coli.