Determination of the midpoint potential of the FAD and FMN flavin cofactors and of the 3Fe-4S cluster of glutamate synthase

Biochemistry
Sergio RavasioM A Vanoni

Abstract

Glutamate synthase is a complex iron-sulfur flavoprotein that catalyzes the reductive transfer of the L-glutamine amide group to C(2) of 2-oxoglutarate, forming two molecules of L-glutamate. The bacterial enzyme is an alphabeta protomer, which contains one FAD (on the beta subunit, approximately 50 kDa), one FMN (on the alpha subunit, approximately 150 kDa), and three different Fe-S clusters (one 3Fe-4S center on the alpha subunit and two 4Fe-4S clusters at an unknown location). To address the problem of the intramolecular electron pathway, we have measured the midpoint potential values of the flavin cofactors and of the 3Fe-4S cluster of glutamate synthase in the isolated alpha and beta subunits and in the alphabeta holoenzyme. No detectable amounts of flavin semiquinones were observed during reductive titrations of the enzyme, indicating that the midpoint potential value of each flavin(ox)/flavin(sq) couple is, in all cases, significantly more negative than that of the corresponding flavin(sq)/flavin(hq) couple. Association of the two subunits to form the alphabeta protomer does not alter significantly the midpoint potential value of the FMN cofactor and of the 3Fe-4S cluster (approximately -240 and -270 mV, respectively), bu...Continue Reading

References

Jul 6, 1990·Biochimica Et Biophysica Acta·M A VanoniB Curti
Nov 1, 1967·The Biochemical Journal·P C Engel, K Dalziel
Mar 15, 1996·European Journal of Biochemistry·M A VanoniB Curti
Sep 1, 2000·Journal of Biological Inorganic Chemistry : JBIC : a Publication of the Society of Biological Inorganic Chemistry·W R HagenF T Robb

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Citations

Oct 7, 2004·Applied and Environmental Microbiology·Marybeth A PyszRobert M Kelly
Oct 23, 2004·Protein Science : a Publication of the Protein Society·Vincenza M CoiroDanilo Roccatano
Mar 27, 2016·Current Opinion in Chemical Biology·John W PetersMichael Ww Adams
Aug 9, 2016·International Journal of Biological Macromolecules·Shan LinYu-Guo Zheng
Jul 26, 2005·Protein Expression and Purification·Francisco J Ruiz-DueñasAngel T Martínez
Dec 29, 2004·Free Radical Research·Anna LewinskaGrzegorz Bartosz
Apr 23, 2002·The Journal of Biological Chemistry·Robert H H van den HeuvelAndrea Mattevi

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