Regulation of two aspartokinase isozymes in Streptococcus bovis.

Streptococcus bovis has been found to contain two distinct aspartokinases that can be separated by gel filtration chromatography. One of these isozymes elutes on Sephadex G-200 gel filtration at a molecular weight greater than 250,000. The molecular weight of the other isozyme is approximately 125,000. The earlier peak of aspartokinase activity is slightly inhibited by meso-diaminopimelate, while the second peak is sensitive to inhibition by lysine. The latter aspartokinase is not formed when the organism is grown in a medium containing more than 1 mM lysine. The level of lysine-sensitive aspartokinase is decreased during the growth cycle, whereas diaminopimelate-sensitive activity is little affected by the growth conditions. The regulatory properties of the two aspartokinases suggest that they may play different physiological roles.

[Regulation of enzymes of the first and last stage of lysine biosynthesis in Streptococcus bovis and Enterococcus faecium]. / Reguliatsiia fermentov pervoi i poslednei stadii biosinteza lizina u Streptococcus bovis i Enterococcus faecium.

Regulation of aspartate kinase and diaminopimelate decarboxylase activities in Streptococcus bovis and Enterococcus faecium cell-free extracts was studied. The levels of synthesis of aspartate kinase and diaminopimelate decarboxylase in both microorganisms are growth-dependent. The synthesis of these enzymes is depressed by lysine, but the activity of aspartate kinase is induced by addition of this amino acid and threonine to the reaction system. Meso-diaminopimelate dehydrogenase activity was not found in the extracts of Streptococcus bovis and Enterococcus faecium. The data excludes the possibility of lysine formation via six enzyme reactions.

[Diaminopimelate pathway for lysine synthesis in Escherichia coli and bacilli]. / Diaminopimelinovyi put' sinteza lizina u Escherichia coli i batsill.

The diaminopimmelate (DAP) pathway for lysine biosynthesis in Escherichia coli and some species of Bacillus are presented in the review. It was shown that the major variations of the DAP pathway of Bacillus subtilis from that described and extensively studied in Escherichia coli exist.