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Ammonia assimilation in Bacillus polymyxa. 15N NMR and enzymatic studies

Kanamori, Keiko and Weiss, Richard L. and Roberts, John D. (1987) Ammonia assimilation in Bacillus polymyxa. 15N NMR and enzymatic studies. Journal of Biological Chemistry, 262 (23). pp. 11038-11045. ISSN 0021-9258.

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Pathways of ammonia assimilation into glutamic acid and alanine in Bacillus polymyxa were investigated by 15N NMR spectroscopy in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthetase, alanine dehydrogenase, and glutamic-alanine transaminase. Ammonia was found to be assimilated into glutamic acid predominantly by NADPH-dependent glutamate dehydrogenase with a Km of 2.9 mM for NH4+ not only in ammonia-grown cells but also in nitrate-grown and nitrogen-fixing cells in which the intracellular NH4+ concentrations were 11.2, 1.04, and 1.5 mM, respectively. In ammonia-grown cells, the specific activity of alanine dehydrogenase was higher than that of glutamic-alanine transaminase, but the glutamate dehydrogenase/glutamic-alanine transaminase pathway was found to be the major pathway of 15NH4+ assimilation into [15N]alanine. The in vitro specific activities of glutamate dehydrogenase and glutamine synthetase, which represent the rates of synthesis of glutamic acid and glutamine, respectively, in the presence of enzyme-saturating concentrations of substrates and coenzymes are compared with the in vivo rates of biosynthesis of [15N]glutamic acid and [alpha,gamma-15N]glutamine observed by NMR, and implications of the results for factors limiting the rates of their biosynthesis in ammonia- and nitrate-grown cells are discussed.

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Additional Information:This work was supported by National Science Foundation Grant DMB85-01617. This is Contribution 7529 from the Gates and Crellin Laboratories of the California Institute of Technology. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact We would like to thank Dr. Francis Martin for helpful discussion and Dr. M. Jane Strouse for assistance in adapting the automatic sample changer program on the Bruker AM-500 spectrometer for ^(15)N NMR work.
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Caltech Gates and Crellin Laboratories of Chemistry7529
Issue or Number:23
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ID Code:6697
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Deposited On:19 Dec 2006
Last Modified:02 Oct 2019 23:35

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