Regulation of lysine- and lysine-plus-threonine-inhibitable aspartokinases in Bacillus brevis.
AUTOR(ES)
Hitchcock, M J
RESUMO
Further studies on the expression of the two aspartokinase activities in Bacillus bovis are presented. Aspartokinase I (previously shown to be inhibited and repressed by lysine) was found to be repressed by diaminopimelate in the wild-type strain. However, in a mutant unable to convert diaminopimelate to lysine, starvation for lysine resulted in an increase in aspartokinase I activity. Thus, lysine itself or an immediate metabolite was the true effector of repression. Aspartokinase II (previously shown to be inhibited by lysine plus threonine) was repressed by threonine. Studies with the parent strain and auxotrophs inidicated that only threonine or an immediate metabolite of threonine was involved in this repression. Methionine and isoleucine were not effectors of any of the detected aspartokinase activities. Apart from inhibition and repression controls, a third as yet undefined regulatory mechanism operated to decrease the levels of both aspartokinases as growth declined, even in mutants in which repression control was absent. In thiosine-resistant, lysine-excreting mutants with elevated levels of aspartokinase, the increase in activity could always be attributed to one enzyme or the other, never both. The existence of separate structural genes for each aspartokinase is therefore suggested.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=293994Documentos Relacionados
- Oxygen-dependent inactivation of gramicidin S synthetase in Bacillus brevis.
- Regulation of Two Aspartokinases in Bacillus subtilis
- Projected structure of unstained, frozen-hydrated T-layer of Bacillus brevis.
- Regulation of Lysine and Threonine Synthesis.
- Cloning and characterization of the gene for a protein thiol-disulfide oxidoreductase in Bacillus brevis.