Succinate Dehydrogenase

Mechanism of a Soluble Fumarate Reductase fromShewanella frigidimarina: A Theoretical Study

“…The electrons are then transferred to quinone, a hydrophobic membrane bound carrier which is reduced to quinol, and for this reason complex II is more correctly named succinate:quinone reductase (SQR). , However, in the absence of oxygen, many microorganisms are able to obtain energy through anaerobic respiratory processes using alternate electron acceptors. , One of the most frequently used is fumarate that is reduced to succinate by quinol:fumarate reductase (QFR). − The importance of QFR can be understood if we consider that not only does it enable bacteria to respire in the absence of oxygen but also it is similar in structure and function to SQR, and is able to functionally replace this enzyme in aerobic respiration when conditions allow it to be expressed anaerobically . SQR and QFR complexes are anchored in the cytoplasmatic membranes of eubacteria such as Escherichia coli ,− and Wolinella succinogenes and in the inner mitochondrial membrane of eukaryotes. − Recently there has been reference to some soluble, periplasmatic, fumarate reductase belonging to Shewanella species. − It is known that some facultative anaerobes, such as Escherichia coli , are able to reversibly oxidize succinate. − Kinetic experiments on Escherichia coli SQR have shown that although the enzyme is capable of both reactions it is more proficient in oxidizing succinate than reducing fumarate at a rate of 40:1 . However, the efficiency of the enzyme in both directions is dependent on the applied potential and pH .…”

Biochemical characterization of a mitochondrial-like organelle from Blastocystis sp. subtype 7

“…Succinate dehydrogenase (EC 1.3.99.1) was assayed using 3.8 mM dichlorophenolindophenol (e534.2 mM 21 cm 21 at 600 nm), 50 mM phenazine methosulfate, 20 mM KCN, in 100 mM potassium phosphate buffer (pH 7.4), and protein (Singer & Kearney, 1963). Sodium succinate (200 mM) was added to start the reaction and the absorbance at 600 nm monitored for 10 min at 37 uC.…”

Crystallization of mitochondrial respiratory complex II from chicken heart: a membrane-protein complex diffracting to 2.0 Å

“…In addition to detergent-solubilized preparations of complex II, a soluble preparation of`succinate dehydrogenase' could be prepared by treating mitochondrial membranes with chaotropes, alkaline pH and/or organic solvent (Bernath et al, 1956;Davis & Hate®, 1971b;Wang et al, 1956). The kinetics and regulatory properties of both soluble and`particulate' succinate dehydrogenase have been studied extensively (Singer et al, 1973). The enzyme has an activated and a`deactivated' state which interconvert slowly with a high activation energy.…”

“…The equilibrium between the two states is affected by substrates and competitive inhibitors, phosphate, some nucleotides and the redox state of the mitochondrial ubiquinone pool. The signi®cance of these regulatory mechanisms is unclear, however, as the amount of activity in the mitochondrion is so high that even in the`deactivated' state SDH seems not to be rate-limiting (Singer et al, 1973). This suggests that complex II may be involved in regulating some other cellular process.…”