Derivation of glycine from threonine in Escherichia coli K-12 mutants.

Escherichia coli AT2046 has been shown previously to lack the enzyme serine transhydroxymethylase and to require exogenous glycine for growth as a consequence. Strains JEV73 and JEV73R, mutants derived from strain AT2046, are shown here to be serine transhydroxymethylase deficient, but able to derive their glycine from endogenously synthesized threonine. Leucine is shown to be closely involved in the regulation of biosynthesis of glycine, to spare glycine in strain AT2046T, to replace glycine in strain JEV73, and to increase threonine conversion to glycine in a representative prototroph of E. coli. An interpretation of strains JEV73 and JEV73R as regulatory mutants of strain AT2046 is given. A hypothesis as to the role of leucine as a signal for nitrogen scavenging is suggested.