Quinol-fumarate reductase

Figure 13.16 (a) Polypeptide fold and (b) electron transfer distances in E. coli quinol-fumarate reductase, (c) intercofactor distances in the Wolinella succinogenes enzyme. (From Iverson et al., 2002. Reproduced by permission of the Journal of Biological Chemistry.)... 

Iverson, T.M., Luna-Chavez, C., Croal, L.R., Cecchini, G. and Rees, D.C. (2002) Crystallographic studies of the Eschericia coli quinol-fumarate reductase with inhibitors bound to the quinol-binding site, J. Biol. Chem., 277, 16124-16130. 

Ohnishi T, Moser CC, Page CC, et al. 2000. Simple redox-linked proton-transfer design new insights from structures of quinol-fumarate reductase. Structure Folding Design 8 R23-R32. 

THE STRUCTURE OF Wolinella succinogenes QUINOL FUMARATE REDUCTASE AND ITS RELEVANCE TO THE SUPERFAMILY OF SUCCINATE QUINONE OXIDOREDUCTASES... 

Flavocytochrome Fumarate Reductase. The flavocytochrome fumarate reductase (Fff) is a soluble periplasmic protein from Shewanella spp. that reduces fumarate but does not oxidize succinate, in contrast to the membrane-bound fumarate reductases that are related to succinate dehydrogenases, and transfer electrons from quinol to fumarate. It is a monomeric protein of 63.8 kDa that is composed of three domains. The N-terminal domain contains four c-type hemes, and the flavin domain contains noncovalently bound FAD and is related to flavoprotein subunits of membrane-bound fumarate reductases and succinate dehydrogenases. There is also a third domain in the flavocytochromes that has considerable flexibility and may be involved in controlling access of substrate to the active site. The macroscopic redox potentials of the fom hemes of Ffr are —102, —146, —196, and -23 8 mV, while that of FAD is —152 mV. The low redox potential of FAD in Ffr compared to that in membrane-bound fumarate reductase (—55 mV) may explain why it is unable to oxidize succinate. 

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