Lysine was found in the vegetative peptidoglycan of Bacillus sphaericus (23 strains), and of the related species Bacillus pasteurii and Bacillus globisporus. None of these organisms formed diaminopimelate epimerase, but all contained diaminopimelate dehydrogenase. All other species of Bacillus studied had diaminopimelate in their walls, and produced diaminopimelate epimerase and N-acetyldiaminopimelate deacetylase, but not diaminopimelate dehydrogenase. One exception, Bacillus macerans, contained all three of these enzymes; diaminopimelate (and no lysine) was found in its walls. A new spectrophotometric assay for diaminopimelate epimerase was developed, which had advantages over the previous methods.
Enzymes were assayed in extracts of Bacillus sphaericus harvested late in the exponential phase from batch cultures in a minimal (acetate plus salts) medium. Aspartokinase was repressed and inhibited by threonine; lysine alone had no effect, though it increased the inhibition (but not the repression) by threonine. Aspartic fl-semialdehyde dehydrogenase was slightly repressed by lysine. Dihydrodipicolinate synthase was inhibited non-competitively by lysine, and dihydrodipicolinate reductase was partly repressed by lysine. Diaminopimelate dehydrogenase (with tetrahydrodipicolinate as substrate) was inhibited by meso-diaminopimelate. Lysine did not repress diaminopimelate decarboxylase, and only slightly inhibited this enzyme. An auxotrophic mutant that required threonine and methionine excreted lysine after growth had stopped with a limited concentration of threonine.
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