Amino acid utilization in bacterial growth. 2. A study of threonine-isoleucine relationships in mutants of Escherichia coli

Abstract

Growth of 4 mutants of E. coli requiring L-threonine is inhibited by L-serine. The inhibition by DL-serine is competitive and is suppressed by D-threonine, alpha-aminobutyric acid, alpha-oxobutyric acid, alpha-oxo-beta-hydroxybutyric acid and L-isoleucine. All the above-listed compounds, except L-isoleucine, exert a sparing effect in the utilization of L-threonine. A mutant requiring either D-threonine, alpha-aminobutyric acid or L-isoleucine is inhibited also by DL-serine, when grown on D-threonine or alpha-aminobutyric acid. These results lead to the hypothesis that L-isoleucine synthesis depends on L-threonine utilization in these mutants.