RESUMEN
The first and the third steps in the aspartate biosynthesis pathway in Streptococcus bovis are catalyzed by two different forms of aspartokinase and a single homoserine dehydrogenase, respectively. These enzymes can be separated by ammonium sulfate fractionation and gel filtration on Sephadex G-200. The two aspartokinase isozymes differ in molecular weights and are subject to differential regulation. The aspartokinase system of S. bovis is characterized by the absence of specific negative allosteric effectors among the end products of the synthesis of amino acids of the aspartic family. Homoserine dehydrogenase, which catalyzes the third step of the aspartic family amino acid synthesis, also has such negative effectors as threonine and methionine. The aspartokinase isozymes do not form multienzyme complexes with homoserine hydrogenase in S. bovis.
Asunto(s)
Aspartato Quinasa/metabolismo , Ácido Aspártico/biosíntesis , Homoserina Deshidrogenasa/metabolismo , Isoenzimas/metabolismo , Streptococcus bovis/enzimología , Regulación Alostérica , Cromatografía en GelRESUMEN
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.
Asunto(s)
Aspartato Quinasa/metabolismo , Proteínas Bacterianas , Carboxiliasas/metabolismo , Enterococcus faecium/enzimología , Lisina/biosíntesis , Streptococcus bovis/enzimología , Aspartato Quinasa/antagonistas & inhibidores , Aspartato Quinasa/biosíntesis , Carboxiliasas/antagonistas & inhibidores , Carboxiliasas/biosíntesis , Catálisis , Sistema Libre de Células , Enterococcus faecium/crecimiento & desarrollo , Enterococcus faecium/metabolismo , Streptococcus bovis/crecimiento & desarrollo , Streptococcus bovis/metabolismoRESUMEN
The effect of threonine and methionine on the growth of and lysine synthesis in Streptococcus bovis st. A024/85 was studied. The character and the degree of manifestation of growth and regulation effects of these amino acids depend on their contents in the fermentation medium. The target in the regulation of lysine biosynthesis is aspartate kinase, whose synthesis is controlled by threonine and methionine. Lysine excretion was stimulated by the addition of a low concentration of dimethylsulfoxide in the medium during fermentation.
Asunto(s)
Lisina/biosíntesis , Streptococcus bovis/metabolismo , Animales , Bovinos , Medios de Cultivo , Dimetilsulfóxido/farmacología , Relación Dosis-Respuesta a Droga , Lisina/efectos de los fármacos , Metionina/farmacología , Rumen/microbiología , Streptococcus bovis/efectos de los fármacos , Streptococcus bovis/aislamiento & purificación , Treonina/farmacología , Factores de TiempoRESUMEN
Integration of the Bacillus subtilis lysA gene cloned on pLP1 plasmid, into the 250 degrees region of the chromosome of this microorganism was performed. Significant differences in the level and character of their expression were shown between lysA gene integrated into the chromosome and plasmid-borne genes. It is suggested that the expression of the lysA gene could be under control of a certain cis-acting factor which is able to promote transcription of the lysA gene and mediate gene specific regulation.
Asunto(s)
Bacillus subtilis/genética , Cromosomas Bacterianos , Genes Bacterianos/genética , Plásmidos/genética , Mapeo Cromosómico , Clonación Molecular , ADN Bacteriano/genética , Ingeniería Genética , Marcadores Genéticos/genéticaRESUMEN
Cloning of Bacillus subtilis DNA fragment with the lysA gene encoding diaminopimelatecarboxylase (EC 4.1.1.20) was done. The cloned gene in poorly expressed both in Escherichia coli and in Bacillus subtilis. Some DNA sequence distant from the lysA gene seems to be necessary for full gene expression, this sequence having been not cloned together with the lysA. The sequence in needed for regulation of the expression as well.
Asunto(s)
Bacillus subtilis/genética , Proteínas Bacterianas , Carboxiliasas/genética , Genes Bacterianos , Sistema Libre de Células , Clonación Molecular , ADN Bacteriano/genética , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Lisina/biosíntesisRESUMEN
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.