Complex III of Electron Transport Chain: Difference between revisions

<applet load='1kyo' size='400' color='black' frame='true' align='right' scene ='Complex_III_of_Electron_Transport_Chain/Sma_525_red/2' name='third'/>The cycle starts with the binding of UQH₂, ubiquinol, to cytochrome b at a Q_P site. In the applet to the right the Q_P 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 <scene name='Complex_III_of_Electron_Transport_Chain/Posit_cytob_closeup/1'>to the ubiquinol</scene> at Q_P.  Binding of the His to UQH₂ reduces its pK, and the [http://en.wikipedia.org/wiki/Ubiquinol UQH₂] loses a proton to become UQH.  The position of Q_P in the complex is such that the proton which is lost <scene name='Complex_III_of_Electron_Transport_Chain/Proton_releas/2'>diffuses to the intermembrane space</scene>.