THE UTILIZATION OF PHENYLALANINE AND TYROSINE DERIVATIVES BY MUTANT STRAINS OF ESCHERICHIA COLI

The production of several mutant strains of Escherichiu coEi which require for growth an exogenous source of particular amino acids (1) has made possible a study of the manner in which individual mutants can use pcptides and other amino acid derivatives for growth.In the present c~ommunioat,ion, data are presented on the utilization of derivatives of phcnylalanine and tyrosine by appropriate mutants of Escherichia ccli.One of the mut.ant strtlins (So.58-278) which requires phenylalanine \V:V obtained by irradiation with x-rays of strain 58, a mutant strain obt:rined previously and characterized by a requirement for biotin (2).Two aclditional strains which require phenylalanine (strains 584899 and 58-6314) and a strain which requires tyrosine (strain 58-5030) were obtained upon exposure of strain 58 to methyl-bis(/%chloroethyl)amine (3).No differences could be observed among the three strains which were unable to synthesize phenylalanine from the constituents of the basal medium (2) and in the present, discussion t,hey will be considered as a single strain, i.e. phenylalanineless.The amino acid requirement of each mutant strain was completely specific; the phen.ylalaninelessstrain grew in the presence of L-phenylalanine but not in the presence of L-tyrosine, and the tyrosineless strain grew in the presence of L-tyrosine but not of L-phenylalanine.For half maximal growth in 24 hours at 30" t'he phenylalanineless strain required, per 10 ml. of medium, approximately 1 X 10e4 mM of phenylalanine or 2 X 10m4 mM of Dr.,-phenylalanine.The amount of L-tyrosine which gave, per 10 ml. of medium, half maximal growth for the tyrosineless skain was 0.9 X 10m4 m&r and the amount of m,-tyrosine was 2.1 X 1O-4 ml1 (Fig. 1).The D antipodes were not utilized for growth and, as may be seen from the data on the nn-amino acids, did not inhibit growth under the experimental conditions employed in this study.In the st.udy of the utilization of derivatives of phenylalanine and tyrosine, these were added to the basal medium, and, if growth occurred, a