This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Cofactors, Prosthetic Groups, Electron Carriers Biosynthesis → Quinol and Quinone Biosynthesis → Rhodoquinone Biosynthesis|
Rhodoquinone (RQ) is a modified ubiquinone, where the methoxyl group in position 3 is replaced by an amino group. The compound was originally isolated from Rhodospirillum rubrum [Glover62, Moore65, Parson65], where is it used for the reduction of fumarate to succinate under anaerobic conditions.
Rhodoquinone is not limited to prokaryotes. It was soon discovered that some eukaryotic parasites such as the nematodes Ascaris suum and Ascaris lumbricoides [Ozawa69, Kassner75], as well as parasitic helminths [Allen73] also contain rhodoquinone, which is essential for fumarate reduction under anaerobic conditions [Kita88]. Later it was shown that rhodoquinone is present in all eukaryotes that reduce fumarate during anoxia, including freshwater snails, mussels, lugworms, and oysters [Van95a].
About This Pathway
The original rhodoquinone isolated from Rhodospirillum rubrum was rhodoquinone-10, with a side chain containing 10 prenyl units (as reported in [Moore65]). rhodoquinone-10 was also detected in several eukaryotes that are subjected to anaerobic conditions, including the liver fluke Fasciola hepatica [Van96a], the mussel Mytilus edulis, the lugworm Arenicola marina, the oyster Crassostrea gigas, and the snail Lymnaea stagnalis [Van95a].
Ubiquinone has beenv shown to be an intermediate in the rhodoquinone pathway of Rhodospirillum rubrum [Brajcich10]. A gene involved in rhodoquinone-10 biosynthesis, named rquA, has been identified in Rhodospirillum rubrum [Lonjers12]. A deletion or mutation of the gene results in absence of rhodoquinone in the cells. The protein shares sequence and predicted secondary structure similarities with class I S-adenosylmethionine (SAM)-dependent methyltransferases.However, the exact role of the enzyme is not yet known.
Brajcich10: Brajcich BC, Iarocci AL, Johnstone LA, Morgan RK, Lonjers ZT, Hotchko MJ, Muhs JD, Kieffer A, Reynolds BJ, Mandel SM, Marbois BN, Clarke CF, Shepherd JN (2010). "Evidence that ubiquinone is a required intermediate for rhodoquinone biosynthesis in Rhodospirillum rubrum." J Bacteriol 192(2);436-45. PMID: 19933361
Kita88: Kita K, Takamiya S, Furushima R, Ma YC, Suzuki H, Ozawa T, Oya H (1988). "Electron-transfer complexes of Ascaris suum muscle mitochondria. III. Composition and fumarate reductase activity of complex II." Biochim Biophys Acta 935(2);130-40. PMID: 2843227
Lonjers12: Lonjers ZT, Dickson EL, Chu TP, Kreutz JE, Neacsu FA, Anders KR, Shepherd JN (2012). "Identification of a new gene required for the biosynthesis of rhodoquinone in Rhodospirillum rubrum." J Bacteriol 194(5);965-71. PMID: 22194448
Parson65: Parson WW, Rudney H (1965). "The biosynthesis of ubiquinone and rhodoquinone from p-hydroxybenzoate and p-hydroxybenzaldehyde in Rhodospirillum rubrum." J Biol Chem 240;1855-63. PMID: 14285535
Van95a: Van Hellemond JJ, Klockiewicz M, Gaasenbeek CP, Roos MH, Tielens AG (1995). "Rhodoquinone and complex II of the electron transport chain in anaerobically functioning eukaryotes." J Biol Chem 270(52);31065-70. PMID: 8537365
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