Editing SDHD (section)

== Function ==
SDHD forms part of the transmembrane [[protein dimer]] with [[SDHC (gene)|SDHC]] that anchors [[Complex II]] to the inner mitochondrial membrane. The SDHC/SDHD dimer provides binding sites for [[ubiquinone]] and water during electron transport at Complex II. Initially, [[SDHA]] oxidizes [[succinate]] via [[deprotonation]] at the [[flavin adenine dinucleotide|FAD]] binding site, leaving [[fumarate]], loosely bound to the active site, free to exit the protein. The electrons derived from succinate tunnel along the [Fe-S] relay in the [[SDHB]] subunit until they reach the [3Fe-4S] [[iron–sulfur cluster]]. The electrons are then transferred to an awaiting [[ubiquinone]] molecule at the active site in the SDHC/SDHD dimer. The O1 [[carbonyl]] oxygen of ubiquinone is oriented at the active site (image 4) by [[hydrogen bond]] interactions with Tyr83 of SDHD. The presence of electrons in the [3Fe-4S] iron sulphur cluster induces the movement of ubiquinone into a second orientation. This facilitates a second hydrogen bond interaction between the O4 carbonyl group of ubiquinone and Ser27 of subunit C. Following the first single electron reduction step, a [[semiquinone]] radical species is formed. The second electron arrives from the [3Fe-4S] cluster to provide full reduction of the ubiquinone to [[ubiquinol]].<ref>{{cite journal | vauthors = Horsefield R, Yankovskaya V, Sexton G, Whittingham W, Shiomi K, Omura S, Byrne B, Cecchini G, Iwata S | title = Structural and computational analysis of the quinone-binding site of complex II (succinate-ubiquinone oxidoreductase): a mechanism of electron transfer and proton conduction during ubiquinone reduction | journal = The Journal of Biological Chemistry | volume = 281 | issue = 11 | pages = 7309–16 | date = March 2006 | pmid = 16407191 | doi = 10.1074/jbc.m508173200 | doi-access = free }}</ref>