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Squalene-hopene cyclase (SHC) () or ''hopan-22-ol hydro-lyase'' is a prokaryotic enzyme in the terpene cyclase/mutase family. It catalyzes the interconversion of an acyclic squalene molecule into a pentacyclic triterpenes hopene and hopanol in the ratio of 5:1. This enzyme catalyses the following chemical reactions. : squalene hop-22(29)-ene : squalene + H2O hopan-22-ol Squalene-hopene cyclase is important because its products, the hopenoids, are very much like sterols in eukaryotes in that they condense lipid membranes and reduce permeability. In the case of prokaryotes, they provide stability in the face of high temperatures and extreme acidity due to the rigid ring structures. Indeed, upregulation of squalene-hopene cyclase occurs in certain bacteria in the presence of hot or acidic environments. == Introduction == Squalene-hopene cyclase is found in a large number of bacteria but is most readily isolated from the thermophilic bacterium ''Alicyclobacillus acidocaldarius''. It catalyses the conversion of the acyclic molecule of squalene into the pentacyclic triterpenes of hopene and hopanol. Squalene-hopene cyclase is thought to be an evolutionary progenitor of many classes of eukaryotic and prokaryotic sterol cyclases. Oxidosqualene cyclases, which are eukaryotic analogs of SHC require oxygen for their reaction demonstrating a much later evolution when the atmosphere began accumulating oxygen. Squalene-hopene cyclase functions in a hypoxic environment suggesting a much earlier presence. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Squalene-hopene cyclase」の詳細全文を読む スポンサード リンク
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