PMID:7832509

Citation	Liao, JC, Chao, YP and Patnaik, R (1994) Alteration of the biochemical valves in the central metabolism of Escherichia coli. Ann. N. Y. Acad. Sci. 745:21-34
Abstract	Although E. coli central metabolism has been studied for several decades, many regulatory features are still unknown. To achieve the goal of rational manipulation of cellular metabolism, it is important to understand how E. coli responds to overexpressed enzymes. By studying the biochemical control of fluxes between PEP, pyruvate, and OAA, we have addressed some fundamental questions that may prove to be essential for applications in metabolic engineering. First, we found that simultaneous overexpression of Pck and Ppc, or Pps alone in the presence of glucose leads to phenotypes consistent with futile cycline. In contrast to our expectation, futile cycling per se does not affect the growth rate significantly. However, excessive futile cycling may cause competitive disadvantage in the natural environment. Overexpression of Pck caused growth inhibition but no futile cycling. Therefore, E. coli controls the expression of gluconeogenic enzymes not only to avoid excessive futile cycling, but also to prevent toxicity effects. In metabolic engineering, futile cycling may be used as a strategy to stimulate metabolism for either production of metabolites or digestion of toxic wastes. Second, we found that the expression levels of Pps and Pck in E. coli are not optimal for growth on pyruvate and succinate, respectively. Overexpression of these enzymes increases the growth rate on pyruvate and on succinate, respectively, indicating that the slow growth rates on these substrates are at least partially caused by the insufficient supply of PEP and its derivatives. Moreover, E. coli also has not optimized the Ppc level for optimal growth yield on glucose in uncontrolled batch cultures. These results demonstrate that the central metabolism is not optimized for growth under defined laboratory conditions. Thus, the possibility exists that adjustment of native enzyme levels in the central metabolism can improve bioreactor performance. Third, we found that overexpression of Pck affects the transcriptional levels of unrelated genes. This example indicates that physiological responses to enzyme (over)expression should be interpreted cautiously, as changing the expression level of a specific enzyme may affect many unlinked genes. Similar results have also been obtained by use of two-dimensional electrophoresis of proteins from E. coli. Although more questions remain to be answered, fast progress in the area of metabolic engineering can be expected in the near future.
Links	PubMed
Keywords	Bacterial Proteins/antagonists & inhibitors; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Carbon/metabolism; Citric Acid Cycle; Escherichia coli/genetics; Escherichia coli/growth & development; Escherichia coli/metabolism; Gene Expression Regulation, Bacterial; Gene Expression Regulation, Enzymologic; Glucose/metabolism; Glycolysis; Phosphoenolpyruvate Carboxykinase (GTP)/antagonists & inhibitors; Phosphoenolpyruvate Carboxykinase (GTP)/genetics; Phosphoenolpyruvate Carboxykinase (GTP)/metabolism; Phosphoenolpyruvate Carboxylase/antagonists & inhibitors; Phosphoenolpyruvate Carboxylase/genetics; Phosphoenolpyruvate Carboxylase/metabolism; Phosphoenolpyruvate Sugar Phosphotransferase System/metabolism; Phosphotransferases (Paired Acceptors)/antagonists & inhibitors; Phosphotransferases (Paired Acceptors)/genetics; Phosphotransferases (Paired Acceptors)/metabolism; Pyruvate Kinase/antagonists & inhibitors; Pyruvate Kinase/genetics; Pyruvate Kinase/metabolism; Pyruvates/metabolism; Pyruvic Acid
edit table

Significance

You can help EcoliWiki by summarizing why this paper is useful

Useful Materials and Methods

You can help Ecoliwiki by describing the useful materials (strains, plasmids, antibodies, etc) described in this paper.

Annotations

<annotationlinks/>

EcoliWiki Links

Add links to pages that link here (e.g. gene, product, method pages)

References

See Help:References for how to manage references in EcoliWiki.