METABOLISM OF GLYCINE AND SERINE IN ESCHERICHIA COLI

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Abstract
The metabolism of strain S, initially classified as a serine auxotroph of E. coli strain K-12, and of strain S/G, an auxotroph responding to either serine or glycine, was studied. Strain S now was shown to grow on exogenous glycine, but its response to glycine appeared to be an adaptive one. The growth of strain S on glycine was influenced by the size and source of the inoculum, the concentration of glycine in the medium, and the presence of aspara-gine and glutamic acid in the medium; high concentrations of asparagine inhibited growth on glycine, and glutamate reversed the inhibition. After adaptation to glycine, strain S appeared to be identical to strain S/G. Strain S grew readily on glycine peptides; this growth response was not adaptive. The main difference between growth on free glycine and on peptide glycine was the relatively faster growth rate permitted by pep-tide glycine. By use of the isotope technique, strain S/G was shown to effect the interconversion of serine and glycine. Both strains S/G and S appeared to be capable of forming serine from glycine, of degrading serine to glycine, and of forming glycine from glucose via a pathway in which serine is not an obligatory intermediate. It was concluded that strain S, unlike strain S/G, is deficient in the mechanism by which free glycine is taken up from the culture medium.

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