The redundant aminotransferases in lysine and arginine synthesis and the extent of aminotransferase redundancy in Escherichia coli.

Aminotransferases can be redundant or promiscuous, but the extent and significance of these properties is not known in any organism, even in Escherichia coli. To determine the extent of redundancy, it was first necessary to identify the redundant aminotransferases in arginine and lysine synthesis, and then complement all aminotransferase-deficient mutants with genes for all aminotransferases. The enzymes with N-acetylornithine aminotransferase (ACOAT) activity in arginine synthesis were ArgD, AstC, GabT and PuuE; the major anaerobic ACOAT was ArgD.

Putrescine catabolism is a metabolic response to several stresses in Escherichia coli.

Genes whose products degrade arginine and ornithine, precursors of putrescine synthesis, are activated by either regulators of the nitrogen-regulated (Ntr) response or σ(S) -RNA polymerase. To determine if dual control regulates a complete putrescine catabolic pathway, we examined expression of patA and patD, which specify the first two enzymes of one putrescine catabolic pathway. Assays of PatA (putrescine transaminase) activity and β-galactosidase from cells with patA-lacZ transcriptional and translational fusions indicate dual control of patA transcription and putrescine-stimulated patA translation.

Pathway and enzyme redundancy in putrescine catabolism in Escherichia coli.

Putrescine as the sole carbon source requires a novel catabolic pathway with glutamylated intermediates. Nitrogen limitation does not induce genes of this glutamylated putrescine (GP) pathway but instead induces genes for a putrescine catabolic pathway that starts with a transaminase-dependent deamination. We determined pathway utilization with putrescine as the sole nitrogen source by examining mutants with defects in both pathways.

Genetics and regulation of the major enzymes of alanine synthesis in Escherichia coli.

Genetic analysis of alanine synthesis in the model genetic organism Escherichia coli has implicated avtA, the still uncharacterized alaA and alaB genes, and probably other genes. We identified alaA as yfbQ. We then transferred mutations in several transaminase genes into a yfbQ mutant and isolated a mutant that required alanine for optimal growth.

Crystal structure of N-succinylarginine dihydrolase AstB, bound to substrate and product, an enzyme from the arginine catabolic pathway of Escherichia coli.

The ammonia-producing arginine succinyltransferase pathway is the major pathway in Escherichia coli and related bacteria for arginine catabolism as a sole nitrogen source. This pathway consists of five steps, each catalyzed by a distinct enzyme. Here we report the crystal structure of N-succinylarginine dihydrolase AstB, the second enzyme of the arginine succinyltransferase pathway, providing the first structural insight into enzymes from this pathway.

Phosphorylation-independent dimer-dimer interactions by the enhancer-binding activator NtrC of Escherichia coli: a third function for the C-terminal domain.

The response regulator NtrC transcriptionally activates genes of the nitrogen-regulated (Ntr) response. Phosphorylation of its N-terminal receiver domain stimulates an essential oligomerization of the central domain. Deletion of the central domain reduces, but does not eliminate, intermolecular interactions as assessed by cooperative binding to DNA.

The Escherichia coli gabDTPC operon: specific gamma-aminobutyrate catabolism and nonspecific induction.

Nitrogen limitation induces the nitrogen-regulated (Ntr) response, which includes proteins that assimilate ammonia and scavenge nitrogen. Nitrogen limitation also induces catabolic pathways that degrade four metabolically related compounds: putrescine, arginine, ornithine, and gamma-aminobutyrate (GABA). We analyzed the structure, function, and regulation of the gab operon, whose products degrade GABA, a proposed intermediate in putrescine catabolism.

Regulation of carbon utilization by sulfur availability in Escherichia coli and Salmonella typhimurium.

Different pleiotropic transcriptional regulators are known to function in the coordination of regulons concerned with carbon, nitrogen, sulfur, phosphorus and iron metabolism, but how expression profiles of these different regulons are coordinated with each other is not known. The basis for the effects of cysB mutations on carbon utilization in Escherichia coli and Salmonella typhimurium was examined. cysB mutations affected the utilization of some carbon sources more than others and these effects could be partially, but not completely, reversed by the inclusion of cysteine or djenkolate in the growth medium.