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.