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Journal of Bacteriology, September 1998, p. 4571-4575, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Pathway Choice in Glutamate Synthesis in Escherichia coli

Robert B. Helling*

Department of Biology, University of Michigan, Ann Arbor, Michigan 48109, and Department of Molecular Biology and Biotechnology, Krebs Institute for Biomolecular Research, University of Sheffield, Sheffield, United Kingdom

Received 15 May 1998/Accepted 5 July 1998

Escherichia coli has two primary pathways for glutamate synthesis. The glutamine synthetase-glutamate synthase (GOGAT) pathway is essential for synthesis at low ammonium concentration and for regulation of the glutamine pool. The glutamate dehydrogenase (GDH) pathway is important during glucose-limited growth. It has been hypothesized that GDH is favored when the organism is stressed for energy, because the enzyme does not use ATP as does the GOGAT pathway. The results of competition experiments between the wild-type and a GDH-deficient mutant during glucose-limited growth in the presence of the nonmetabolizable glucose analog alpha -methylglucoside were consistent with the hypothesis. Enzyme measurements showed that levels of the enzymes of the glutamate pathways dropped as the organism passed from unrestricted to glucose-restricted growth. However, other conditions influencing pathway choice had no substantial effect on enzyme levels. Therefore, substrate availability and/or modulation of enzyme activity are likely to be major determinants of pathway choice in glutamate synthesis.

* Mailing address: Department of Biology, University of Michigan, Ann Arbor, MI 48104-1048. Phone: (734) 764-1455. Fax: (734) 647-0884. E-mail: helling{at}umich.edu.

Journal of Bacteriology, September 1998, p. 4571-4575, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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