Question

Select the single best answer. To what class of enzymes does succinate dehydrogenase belong? Explain your answer. Succinate dehydrogenase is an oxodoreductase, because it catalyzes the oxidation of succinate to fumarate. Succinate dehydrogenase is a transferase, because it catalyzes, the oxidation of isoitrate to a ketoglutarate. Succinate dehydrogenase is a transferase, because if catalyzes the transfer of a phosphoryl group from GTP to ADP to make ATP. Succinate dehydrogenase is a hydrolase, because it catalyzes the addition of H_2 O to the double bond of fumarate to give malate.

Answer 1

succinate dehydrogenase is an oxidoreductase, because it catalyzes the oxidation of succinate to fumarate with the reduction of ubiquinone to ubiquinol. mechanism explained below [1].

[1]. Current Opinion in Plant Biology 2013, 16:344–349

Inter-membrane space SDH3 SDH4 Inner-membrane Heme eįơ Matrix SDH2 3x[Fe-S] Frataxin Heme SDH2 Fe-S-SDH2 SDH1 FAD-SDH1 ESDH1 SDHAF1 FAD FADH2 SDHAF2 OAA ATP Succinate Fumarate malonate Current Opinion in Plant Biology SDH composition, assembly factors and inhibitors. The plant mitochondrial succinate dehydrogenase (SDH, complex II), like its mammalian counterpart, is composed of four subunits: two hydrophilic matrix facing proteins (SDH1 and SDH2) and two largely hydrophobic proteins (SDH3 and SDH4) anchoring the complex in the membrane. SDH1 is a flavoprotein containing a covalently bound FAD, SDH2 is an iron-sulfur (Fe-S) protein which contains three Fe-S clusters. SDH3 and 4 are two integral membrane proteins that binding heme to form the b type cytochrome. In addition, the plant mitochondrial SDH complex contains four plant-specific hydrophilic subunits (SDH5-8) with unknown functions. Two SDH assembly factors, SDHAF1 and SDHAF2, are required for insertion of Fe-S and FAD into SDH2 and SDH1, respectively. Frataxin has a role in Fe-S and/or heme synthesis for SDH. During the oxidation of succinate to form fumarate, electrons (e are passed through FAD, Fe S centres and then reduce ubiquinone (Q) to ubiquinol (QH2). The succinate pocket is acted upon by substrate-level inhibitors (such as the succinate- analogues: malonate, malate, oxaloacetate (OAA) and also by ATP that activates the enzyme by inhibitor removal. A different class of inhibitors (SDHD bind in the ubiquinone pocket (e.g., carboxin, which is used as a fungicide on crop plants