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BY-NC-ND 3.0 license Open Access Published by De Gruyter June 2, 2014

Dissociation of FAD from the NAD(P)H-Nitrate Reductase Complex from Ankistrodesmus braunii and Role of Flavin in Catalysis

  • Miguel A. De la Rosa , Antonio J. Márquez and José M. Vega

Ankistrodesmus braunii NAD(P)H-nitrate reductase is a complex hemoflavomolybdoprotein composed by eight similar subunits. The flavin prosthetic group, identified as FAD, is essential for the NAD(P)H-dependent activities of the complex, and is located before the heme chromo- phore in the enzyme electron transport chain from reduced pyridine nucleotides to nitrate.

Fluorescence studies indicate that nitrate reductase can dissociate about 80% of its FAD by incubation at room temperature, the flavin dissociation being followed by a parallel decrease of NADH-nitrate reductase activity. Dissociation of FAD from the protein is easily increased by dilution or prolonged dialysis of the enzyme preparations. However, exogenous FAD specifically prevents the dissociation of enzyme-bound flavin, and protects the NAD(P)H-dependent activities. The Km for FAD, as a protector of NADH-cytochrome c reductase activity, is 4 nᴍ. In addition, dithioerythritol also prevents the flavin dissociation, and therefore the presence of free sulphydryl groups in the FAD-domain is suggested.

FAD-depleted nitrate reductase, obtained by several methods, is unable to recover its original activity when incubated in the presence of FAD alone or with thiols.

Received: 1981-7-20
Revised: 1981-10-1
Published Online: 2014-6-2
Published in Print: 1982-2-1

© 1946 – 2014: Verlag der Zeitschrift für Naturforschung

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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