Enzyme: nitrate reductase A (EC 126.96.36.199).
Evidence for two different electron transfer pathways in the same enzyme, nitrate reductase A from Escherichia coli
Article first published online: 18 MAY 2004
European Journal of Biochemistry
Volume 271, Issue 12, pages 2400–2407, June 2004
How to Cite
Giordani, R. and Buc, J. (2004), Evidence for two different electron transfer pathways in the same enzyme, nitrate reductase A from Escherichia coli. European Journal of Biochemistry, 271: 2400–2407. doi: 10.1111/j.1432-1033.2004.04159.x
Present address: Faculté de Pharmacie, Université de la Méditerranée, 13385 Marseille Cedex 05, France.
- Issue published online: 4 JUN 2004
- Article first published online: 18 MAY 2004
- (Received 17 March 2004, revised 8 April 2004, accepted 14 April 2004)
- cytochrome b;
- electron transfer;
- Escherichia coli;
- nitrate reductase A;
In order to clarify the role of cytochrome in nitrate reductase we have performed spectrophotometric and stopped-flow kinetic studies of reduction and oxidation of the cytochrome hemes with analogues of physiological quinones, using menadione as an analogue of menaquinone and duroquinone as an analogue of ubiquinone, and comparing the results with those obtained with dithionite. The spectrophotometric studies indicate that reduction of the cytochrome hemes varies according to the analogue of quinone used, and in no cases is it complete. Stopped-flow kinetics of heme oxidation by potassium nitrate indicates that there are two distinct reactions, depending on whether the hemes were previously reduced by menadiol or by duroquinol. These results, and those of spectrophotometric studies of a mutant lacking the highest-potential [Fe-S] cluster, allow us to propose a two-pathway electron transfer model for nitrate reductase A from Escherichia coli.