Complex III of Electron Transport Chain: Difference between revisions

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Karl Oberholser, Eran Hodis, Jaime Prilusky, Alexander Berchansky, Michal Harel

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 == Structure of three active components ==
-Each cytochrome b contains<scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_b/2'> two hemes</scene>. Identify each of the hemes by hovering the curser over an atom of the heme.  Hem 501 and Hem 502 are in one cytochrome b, and Hem 521 and Hem 522 are in the other one.  The two hemes in each cytochrome b are in different environments and therefore have different properties, e.g. reduction potential. Hemes 501 & 521 have a lower potential than the other two and are called b<sub>L</sub> for low potential, and the other two are called b<sub>H</sub> for high potential. Each of the cytochrome b's have two binding sites for substrate. Ubiquinol binds at one of the sites, Q<sub>P</sub>, and the inhibitor stigmatellin binds at this site in both cytochrome b's (<scene name='Complex_III_of_Electron_Transport_Chain/Sma_blink_cyto_b/2' target='second'>Blink stigmatellin</scene> in the applet below)(<scene name='Complex_III_of_Electron_Transport_Chain/Sma_cyto_b/1' target='second'>return to view of the inhibitor stigmatellin</scene>), and the site is adjacent to the b<sub>L</sub> heme. The other site, Q<sub>N</sub>, binds [[Coenzyme_Q10|ubiquinone]], and <scene name='Complex_III_of_Electron_Transport_Chain/Surface_qn/2' name='second'>this surface</scene> outlines the site which is adjacent to the b<sub>H</sub> heme.  antimycin A.
+Each cytochrome b contains<scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_b/2'> two hemes</scene>. Identify each of the hemes by hovering the curser over an atom of the heme.  Hem 501 and Hem 502 are in one cytochrome b, and Hem 521 and Hem 522 are in the other one.  The two hemes in each cytochrome b are in different environments and therefore have different properties, e.g. reduction potential. Hemes 501 & 521 have a lower potential than the other two and are called b<sub>L</sub> for low potential, and the other two are called b<sub>H</sub> for high potential. Each of the cytochrome b's have two binding sites for substrate. Ubiquinol binds at one of the sites, Q<sub>P</sub>, and the inhibitor stigmatellin binds at this site in both cytochrome b's (<scene name='Complex_III_of_Electron_Transport_Chain/Sma_blink_cyto_b/2' target='second'>Blink stigmatellin</scene> in the applet below)(<scene name='Complex_III_of_Electron_Transport_Chain/Sma_cyto_b/2' target='second'>return to view of the inhibitor stigmatellin</scene>), and the site is adjacent to the b<sub>L</sub> heme. The other site, Q<sub>N</sub>, binds [[Coenzyme_Q10|ubiquinone]], and <scene name='Complex_III_of_Electron_Transport_Chain/Surface_qn/2' name='second'>this surface</scene> outlines the site which is adjacent to the b<sub>H</sub> heme.  antimycin A.
-<applet load='1kyo' size='400' color='black' frame='true' align='right' scene ='Complex_III_of_Electron_Transport_Chain/Sma_cyto_b/1' name='second'/>Each <font color='#0000CD'>cytochrome c1</font> contains <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1/2'>a heme</scene>. Viewing <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_top/2' target='second'>cyto c1 in spacefill</scene> as it would be seen from the intermembrane space, there is an opening in the center of the dimeric structure through which one can see the gray hemes of the cyto b's. Also seen in this view is the gray heme embedded in each of the cyto c1's showing that the heme is located in a crevice which is open to the intermembrane space and to the <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_side_open/1'>side facing the Rieske protein</scene> (heme oxygens are seen). These openings of the crevice permits the cyto c1 heme to make contact with the Rieske protein and with cytochrome c when it binds to the <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_top/2'>surface of cyto c1</scene>. There are <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_neg_res/1'>negatively charged acidic residues</scene> which attrack the complementary positive charges on cytochrome c, a basic protein. <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c/3'>Cytochrome c (colored cyan)</scene> bound to one cyto c1 showing that the hemes of the two cytochromes are in close contact.  The <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c_transparent/1'>two hemes</scene> seen through transparent spacefill.
+<applet load='1kyo' size='400' color='black' frame='true' align='right' scene ='Complex_III_of_Electron_Transport_Chain/Sma_cyto_b/2' name='second'/>Each <font color='#0000CD'>cytochrome c1</font> contains <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1/2'>a heme</scene>. Viewing <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_top/2' target='second'>cyto c1 in spacefill</scene> as it would be seen from the intermembrane space, there is an opening in the center of the dimeric structure through which one can see the gray hemes of the cyto b's. Also seen in this view is the gray heme embedded in each of the cyto c1's showing that the heme is located in a crevice which is open to the intermembrane space and to the <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_side_open/1'>side facing the Rieske protein</scene> (heme oxygens are seen). These openings of the crevice permits the cyto c1 heme to make contact with the Rieske protein and with cytochrome c when it binds to the <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_top/2'>surface of cyto c1</scene>. There are <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c1_neg_res/1'>negatively charged acidic residues</scene> which attrack the complementary positive charges on cytochrome c, a basic protein. <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c/3'>Cytochrome c (colored cyan)</scene> bound to one cyto c1 showing that the hemes of the two cytochromes are in close contact.  The <scene name='Complex_III_of_Electron_Transport_Chain/Hem_cyto_c_transparent/1'>two hemes</scene> seen through transparent spacefill.
 <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>. The head bending at the hinge region can be in one of three possible positions. (See references 1,2,3 in the Index for details.). Here it is shown in the Int (Intermediate) position