PMID: 6109546Dec 9, 1980Paper

Subunit interaction during catalysis: ammonium ion modulation of catalytic steps in the Escherichia coli glutamine synthetase reaction

Biochemistry
G S Bild, P D BOYER

Abstract

A new approach for assessing if catalytic cooperativity may occur between subunits has been applied to Escherichia coli glutamine synthetase. The extent of oxygen exchange between bound [18O]glutamate and phosphate per molecule of glutamine formed was evaluated at various NH4+ concentrations. This allows calculation of the minimum number of reaction reversals in which bound glutamine is converted to bound glutamate prior to release of glutamine. At 1000 microM NH4+ no detectable reversals occurred, and only one glutamate oxygen appeared in product phosphate as required by the reaction mechanism. However, at 10 microM NH4+ over 15 reversals of bound glutamine formation occurred. Controls showed that under the experimental conditions free glutamine does not become significantly involved in exchange and, therefore, the reversal of the oxygen exchange steps appears to be limited to bound glutamine. In contrast to the effect seen with NH4+, adenosine 5'-triphosphate concentration appears to modulate the exchange of oxygen between glutamate and phosphate only slightly. These findings are interpreted as showing that NH4+ either promotes the dissociation of one of the reaction products or decreases the participation of bound products i...Continue Reading

References

Dec 14, 1978·Biochemical and Biophysical Research Communications·M S BalakrishnanJ J Villafranca
Aug 1, 1979·Proceedings of the National Academy of Sciences of the United States of America·D D HackneyP D Boyer
Mar 1, 1979·Analytical Biochemistry·R HamiltonM McCabe
Feb 1, 1976·Archives of Biochemistry and Biophysics·R Adolfsen, E N Moudrianakis
Sep 26, 1966·Archives of Biochemistry and Biophysics·C A WoolfolkE R Stadtman
Nov 25, 1980·Biochemistry·T D Meek, J J Villafranca

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Citations

Apr 12, 2006·Proceedings of the National Academy of Sciences of the United States of America·Chong YuanWilliam L Smith
Apr 1, 1981·Proceedings of the National Academy of Sciences of the United States of America·W T WolodkoW A Bridger
Apr 6, 2002·Nutrition·Malcolm WatfordPriya Raman
Sep 10, 1985·Biochemistry·D D Clark, J J Villafranca

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