Complex III of Electron Transport Chain: Difference between revisions
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<scene name='Complex_III_of_Electron_Transport_Chain/Fes/1'>Fe/S center</scene> is in the head of the Rieske protein. Each of the Fe/S centers is complexed with <scene name='Complex_III_of_Electron_Transport_Chain/Fes_his/1'>two His</scene>. As a result of bending at the hinge region the head can be in one of three possible positions. Here it is shown in the Int (Intermediate) position. It is called Int because it is intermediate between the other two positions. From the Int position the head can move toward cyto b where one of the His which is complexed with the Fe/S makes contact with the substrate binding at Q<sub>P</sub> in cytochrome b. In the third position head the other His complexed with Fe/S becomes hydrogen bonded to a carboxylate oxygen of the heme in c1. | <scene name='Complex_III_of_Electron_Transport_Chain/Fes/1'>Fe/S center</scene> is in the head of the Rieske protein. Each of the Fe/S centers is complexed with <scene name='Complex_III_of_Electron_Transport_Chain/Fes_his/1'>two His</scene>. As a result of bending at the hinge region the head can be in one of three possible positions. Here it is shown in the Int (Intermediate) position. It is called Int because it is intermediate between the other two positions. From the Int position the head can move toward cyto b where one of the His which is complexed with the Fe/S makes contact with the substrate binding at Q<sub>P</sub> in cytochrome b. In the third position head the other His complexed with Fe/S becomes hydrogen bonded to a carboxylate oxygen of the heme in c1. | ||
== Q Cycle == | |||
<applet load='1kyo' size='400' color='black' frame='true' align='right' scene ='Complex_III_of_Electron_Transport_Chain/Sma_525_red/1' name='third'/>The cycle starts with the binding of UQH<sub>2</sub>, ubiquinol, to cytochrome b at a Q<sub>P</sub> site. In the applet to the right the Q<sub>P</sub> site is binding <font color=red>stigmatellin</font>. This binding causes the Rieske protein to flex at the hinge region rotating the Fe/S head so that the His which is bound to the Fe/S also binds to the UQH<sub>2</sub> at Q<sub>P</sub>. Binding of the His to UQH<sub>2</sub> reduces its pK, and the quinol loses a proton. The position of Q<sub>P</sub> in the complex is such that the proton which is lost diffuses to the intermembrane space. | |||