Succinate Dehydrogenase

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I. Introduction

Succinate dehydrogenase is also known as complex II in electron transport. The 4 subunit complex is bound in the mitochondrial membrane. Succinate dehydrogenase acts by oxidizing succinate into fumarate while passing electrons on to FAD which then is reduced to FADH2. FADH2 then passes its electrons onto the iron-sulfur centers found in the second subunit of the protein. After passing through the iron-sulfur centers, electrons are then passed into either a heme molecule or ubiquinone where they are transported out of this complex and onto the next step of electron transport. This chime page is made to be used in sequence. It starts out by showing the entire protein in different views then shows each subunit and any associated ligands with the subunit. The ligands are shown separately to illustrate how the electron flow is linear through this complex from the cytoplasmic side to the inside of the mitochondria. The final three sections show in detail each step of electron transport through this complex.

For more information see Biochemistry Online: Chapter 8B -
ATP and Oxidative Phosphorylation Reactions

II. General Structure

Chain A

This is the flavoprotein subunit of succinate dehydrogenase.
Chain A with FAD

This is the flavoprotein subunit of succinate dehydrogenase with the FAD shown.
Chain B

This is the Iron-Sulfur protein of succinate dehydrogenase.
Chain B with Iron-Sulfur Centers

This is the Iron-Sulfur protein of succinate dehydrogenase with the iron-sulfur centers shown.
Chain C

This is the Cytochrome B-556 subunit of succinate dehydrogenase. Using the cartoon view on this you can see the helices that span the mitochondrial membrane.
Chain D

This is the hydrophobic membrane anchor protein of succinate dehydrogenase. By viewing this in the cartoon view, you can see the membrane spanning helices that anchor the protein.

This view shows all the ligands in the order of electron flow. By clicking on each atom or group of atoms, you can differentiate between them by looking at the bottom of the page.

Cartoon representation of structures with ligands
FAD and Oxaloacetate

This shows the first step of electron transport through this complex. After succinate is oxidized to fumarate, electrons are passed on to FAD reducing it to FADH2. Succinate is normally bound where the oxaloacetate is bound in this view (oxaloacetate is highlighted in the thicker wireframe). Oxaloacetate is shown here as an inhibitor of this complex.

Iron-Sulfur Centers

This shows the three Iron-Sulfur centers in the complex. Together these centers act as the second step of electron transport in this complex. Electrons are passed on from FADH2 to the iron-sulfur complexes. Each center is slightly different to represent the flow of electrons from one center to the next.

Heme, DNP, and surrounding residues

This shows the heme group and surrounding residues binding to DNP. In the spot where DNP is bound, Ubiquinone normally binds to carry electrons on to the next complex. In this view, DNP is acting as an inhibitor by binding to the same site as Ubiquinone (DNP is shown in the thicker wireframe).