Succinate quinone oxidoreductases

Hederstedt L, Ohnishi T (1992) Progress in succinate quinone oxidoreductase research. In Ernster L (ed) Molecular mechanisms in bioenergetics. Elsevier, Amsterdam, pp 163-198 Henze K, Martin W (2003) Evolutionary biology essence of mitochondria. Nature 426 127-128 Hoffmeister M, van der Klei A, Rotte C, van Grinsven KW, Van Hellemond JJ, Henze K, Tielens AGM, Martin W (2004) Euglena gracilis rhodoquinone ubiquinone ratio and mitochondrial proteome differ under aerobic and anaerobic conditions. J Biol Chem 279 22422-22429... 

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

Succinate quinone oxidoreductases (EC 1.3.5.1 Hagerhall, 1997 Lancaster, 2002a,b) are enzymes that couple the two-electron oxidation of succinate to fumarate (reaction 1) to the two-electron reduction of quinone to quinol (reaction 2). 

They can also catalyze the opposite reaction, the coupling of quinol oxidation to quinone to the reduction of fumarate to succinate (Lemma et al., 1991). The m-configuration isomer of fumarate, maleinate, is neither produced in the oxidation reaction nor consumed as a substrate in the reduction reaction, i.e, the reaction is stereospecific in both directions. Depending on the direction of the reaction catalyzed in vivo, the members of the superfamily of succinate quinone oxidoreductases... 

Lancaster CR (2002) Succinate quinone oxidoreductases an overview. Biochimica et Bio physica Acta 1553,1-6. 

A clearer picture has emerged for Complex II and crystal sfructures are available for the E. coli succinate quinone oxidoreductase (SQR) and closely related bacterial quinol frnnarate oxidoreductases (QFR) that catalyze the reverse reaction in order to use frnnarate as a terminal electron donor in anaerobic respiration. The sfructure of the SQR monomer showing the location of the redox cofactors is shown in Figure 7. The [2Fe-2S] + + (Tim = 4-10 mV), [4Fe-ASf+ + ( = -175 mV) and [3Fe S]+ ° Em = +65 mV) clusters in the SdhB subunit provide a linear electron transport chain for transferring electrons from the... 

The membrane-bound cytochrome 655s (Bacillus subtilis) contains, according to secondary structure predictions, five transmembrane helices. It functions to anchor two other subunits of the succinate quinone oxidoreductase complex (complex II, E.C. 1.3.5.1) in the cytoplasmic membrane (68). The 1.3-2.0 hemes per covalently bound flavin have been found with the isolated enzyme. The amino acid residues that bind the heme between the a-helices are likely bis(histidine). The EPR and NIR MCD spectra are consistent with this because the EPR spectra show a g value of 3.4 with a HALS lineshape, and the MCD spectra show a low-spin CT band at 1600 nm with Ae of 380 M cm at 4.2 K and 5 T (69). This appears to be another example of a bis(histi-dine)-coordinated heme with near perpendicular alignment of the ligands. 

Succinate quinone oxidoreductases (SQORs) refer collectively to succinateiquinone reductases (SQRs) and quinohfumarate reductases (QFRs) (Equation (11)). 

Complex II is the succinate dehydrogenase of the tricarboxylic acid, or Krebs, cycle and catalyzes the oxidation of succinate to fumarate, coupled to the reduction of UQ to ubiquinol. It is part of a large family of related succinate quinone oxidoreductases and quinol fumarate oxidoreductases found in bacteria and mitochondria that have been classified based on subunit structure, number of cytochrome b haem centers and class of quinone substrate [77, 78]. The mitochondrial form belongs to the class that has a single h type haem bound to one of... 

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