File:P450cycle.svg
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原始文件 (SVG文件,尺寸为9,240 × 6,968像素,文件大小:38 KB)
摘要
此图表或文件名的实际准确度存在争议。
原因:See https://en.wikipedia.org/wiki/User_talk:Slashme/Archive_6#P450_Mechanism - not completely useless, but should be used with care until it's fixed. For usage see: |
描述P450cycle.svg |
English: ==The P450 catalytic cycle==
1: The substrate binds to the active site of the enzyme, in close proximity to the heme group, on the side opposite to the peptide chain. The bound substrate induces a change in the conformation of the active site, displacing a water molecule from the distal axial coordination position of the heme iron[1] changing the state of the heme iron from low-spin to high-spin[2]. This gives rise to a change in the spectral properties of the enzyme, with an increase in absorbance at 390~nm and a decrease at 420~nm. This can be measured by difference spectrometry and is referred to as the "type~I" difference spectrum (see inset graph in figure). Some substrates cause an opposite change in spectral properties, a "reverse type~I" spectrum, by processes that are as yet unclear. Inhibitors and certain substrates that bind directly to the heme iron give rise to the type~II difference spectrum, with a maximum at 430~nm and a minimum at 390~nm (see inset graph in figure). If no reducing equivalents are available, this complex remains stable, allowing the degree of binding to be determined from absorbance measurements in vitro[3] 2: The change in the electronic state of the active site favours the transfer of an electron from NAD(P)H[4]. This takes place via the electron transfer chain, as described above, reducing the ferric heme iron to the ferrous state. 3: Molecular oxygen binds covalently to the distal axial coordination position of the heme iron. The cysteine ligand is a better electron donor than histidine, with the oxygen consequently being activated to a greater extent than in other heme proteins. However, this sometimes allows the bond to dissociate, the so-called "decoupling reaction", releasing a reactive superoxide radical, interrupting the catalytic cycle[1]. 4: A second electron is transferred via the electron-transport system, reducing the dioxygen adduct to a negatively charged peroxo group. This is a short-lived intermediate state. 5: The peroxo group formed in step 4 is rapidly protonated twice by local transfer from surrounding amino-acid side chains, releasing one mole of water, and forming a highly reactive iron(V)-oxo species[1]. 6: Depending on the substrate and enzyme involved, P450 enzymes can catalyse any of a wide variety of reactions. A hypothetical hydroxylation is shown in this illustration. After the product has been released from the active site, the enzyme returns to its original state, with a water molecule returning to occupy the distal coordination position of the iron nucleus. S An alternative route for mono-oxygenation is via the "peroxide shunt": interaction with single-oxygen donors such as peroxides and hypochlorites can lead directly to the formation of the iron-oxo intermediate, allowing the catalytic cycle to be completed without going through steps 3, 4 and 5[3]. A hypothetical peroxide "XOOH" is shown in the diagram. C: If carbon monoxide (CO) binds to reduced P450, the catalytic cycle is interrupted. This reaction yields the classic CO difference spectrum with a maximum at 450 nm.
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日期 | |
来源 | M.Sc. Thesis, David Richfield (User:Slashme) |
作者 |
英语维基百科的Slashme When using this image in external works, it may be cited as follows:
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许可协议
Public domainPublic domainfalsefalse |
我,本作品著作权人,释出本作品至公有领域。这适用于全世界。 在一些国家这可能不合法;如果是这样的话,那么: 我无条件地授予任何人以任何目的使用本作品的权利,除非这些条件是法律规定所必需的。 |
此文件中描述的项目
描繪內容
著作权持有者释出至公有领域 简体中文(已转写)
3月 2008
文件历史
点击某个日期/时间查看对应时刻的文件。
日期/时间 | 缩略图 | 大小 | 用户 | 备注 | |
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当前 | 2012年4月22日 (日) 15:07 | 9,240 × 6,968(38 KB) | Slashme | {{Information |Description ={{en|1====The P450 catalytic cycle== 1: The substrate binds to the active site of the enzyme, in close proximity to the heme group, on the side opposite to the peptide chain. The bound substrate induces a change in the ... | |
2012年4月22日 (日) 14:49 | 没有缩略图 | 9,240 × 6,968(38 KB) | Slashme | Corrected peroxide shunt arrow. | |
2008年7月5日 (六) 10:34 | 9,240 × 6,968(35 KB) | Slashme | {{Information |Description={{en|1===The P450 catalytic cycle== 1: The substrate binds to the active site of the enzyme, in close proximity to the heme group, on the side opposite to the peptide chain. The bound substrate induces a change in the conforma |
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