SUMMARY: Extracts of Bacillus sphaericus NCTC 9602 catalysed the formation of -diaminopimelate from aspartic β-semialdehyde plus pyruvate, or from dihydrodipicolinate, even though no activities of tetrahydrodipicolinate acetylase (or succinylase) nor -acetyl-(or -succinyl-)-diaminopimelate deacylase nor diaminopimelate epimerase were found. However, -diaminopimelate -dehydrogenase was present, and had very high activity at pH 7.5 in the direction of synthesis of -diaminopimelate from tetrahydrodipicolinate. A lysine-requiring mutant of lacked diaminopimelate dehydrogenase, and this enzyme reappeared in a revertant that grew without lysine. Other lysine-requiring auxotrophs were defective in dihydrodipicolinate synthase or dihydrodipicolinate reductase or diaminopimelate decarboxylase, but had diaminopimelate dehydrogenase. Diaminopimelate dehydrogenase is not important in the assimilation of ammonia. Mutants that lack this enzyme or else cannot make one of its substrates (tetrahydrodipicolinate) still grow rapidly in minimal medium (plus 0.7 mM--lysine) containing ammonium chloride (36 mM) as the only major source of nitrogen. The wild-type grew with -glutamine, but not with glutamate or lysine as sole source of nitrogen.


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