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From Proteopedia

Succinate dehydrogenase

Citric Acid Cycle: 1 acetyl-CoA in; 2 CO2, 3 NADH, 1 FADH2, 1 ATP out. With about a million intermediate steps that underclass pre-med and all other science majors know little about and care even less. But for when you need to get into more detail . . .

Seen here is the of succinate dehydrogenase, the component of the citric acid cycle responsible for conversion of succinate to fumarate. It is a tetrameric protein found on the inner membrane of the mitochondria.

As can be seen in the image above, the of the enzyme is composed of alpha helices (purple) and beta sheets (pink) connected by nonrepetitive structure.

Most secondary structure is held in place by backbone (orange), as illustrated here. To make bonds more obvious, they are also shown for the second copy of the protein in the dimer. It is impossible to tell based upon hydrogen bond locations at this zoom whether the beta sheets run parallel or antiparallel. No disulfide bonds are present in the structure.

Both residues are present in succinate dehydrogenase. Again, both the full structure and the residues alone are shown.

Solvating water is present around multiple chains (white) in succinate dehydrogenase. Shown here is the (blue) solvating chain A.

Ligands interact with succinate dehydrogenase in a multitude of locations for a veritable plethora of reasons. Shown here is one in the A chain (lime green). This non-hydrolyzable ligand interacts with uncharged side chains; namely, valine.

One (yellow) is found in succinate dehydrogenase, located in the A chain. Please note that the active site consists of one valine residue, so it is very tiny here. It is located in the upper right of the enzyme if rotation is paused before beginning.

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