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Diaminopimelic acid, which is widely distributed in bacteria, is converted into lysine by a specific decarboxylase (Work & Dewey, 1953; Dewey, Hoare & Work, 1954; Antia, Hoare & Work, 1957), and it has been suggested as an immediate precursor of lysine in some bacteria. A mutant of Escherichia coli deficient in the decarboxylase requires lysine for growth and accumulates diaminopimelic acid in the growth medium when lysine is restricted (Dewey & Work, 1952; Davis, 1952). As little is known of the biosynthesis of diaminopimelic acid, the incorporation of various precursors into this extracellular diaminopimelic acid is of interest. Abelson and his colleagues, using the isotopicdilution technique with E. coli B, suggested that some of the carbon atoms of intracellular diaminopinelic acid and lysine may be derived from aspartic acid (Abelson, 1954; Abelson, Bolton, Britten, Cowie & Roberts, 1953). Direct proof of the incorporation of aspartic acid into diaminopimelic acid was obtained by Gilvarg (1958) with cell-free extracts of E. coli mutant 26-26, which synthesized diaminopimelic acid from aspartic acid and pyruvate or glutamate in the presence of magnesium, adenosine triphosphate, diphosphopyridine nucleotide and triphosphopyridine nucleotide. N-Succinyl-L-diaminopimelic acid was identified as a precursor of diaminopimelic acid in another mutant, and the portion of the diaminopimelic acid molecule derived from aspartate was located (Gilvarg, 1957; Gilvarg, Edelman & Kindler, 1958). We have now obtained evidence that most, but not all, of the cellular lysine of E. coli 9637 is derived directly from diaminopimelic acid. This evidence was obtained by the study, described in the next paper (Meadow & Work, 1959), of the incorporation of [14C]diaminopimelic acid or [14C]lysine into mutants of E. coli which required either or both of these amino acids for growth. The labelled diaminopimelic acid was extracted as described in this paper from the culture filtrate of a * Beit Memorial Fellow. t Present address: Institut Pasteur, Paris. lysine-requiring mutant of E. coli grown with suboptimum amounts of lysine. This method, which is that normally used for the production of diaminopimelic acid both in the laboratory (Work & Denman, 1953; Wright & Cresson, 1953) and on an industrial scale (Casida, 1956), gives a mixture of the me8oand LL-isomers (Hoare & Work, 1955). Perry & Foster (1955) used this method to prepare [14C]diaminopimelic acid with a hydrolysate of a radioactive alga, Scenede8mus obliques, as source of radioactivity. In our experiments the labelling was provided by [14C]glucose. The incorporation of radioactivity both into this extracellular diaminopimelic acid and into that of the cells was compared when the mutant was also grown with trace amounts of other 14C-labelled metabolites to determine whether the diaminopimelic acid accumulating in the growth medium under conditions of lysine-deficiency was derived from the same precursors as the intracellular diaminopimelic acid.

Biosynthesis of diaminopimelic acid and lysine in Escherichia coli. 2. Incorporation of [14C]diaminopimelic acid, lysine and glucose