Cytochrome C oxidase is a molecule that none of us air-breathing creatures can live without. It's also really interesting. This protein complex is a dimer of two smaller complexes. Each of the smaller complexes contains 13 different proteins and two heme groups.
The two heme groups are both part of the cytochrome c oxidase subunit I protein. The DNA sequence of this protein is used for many types of DNA barcoding.
The above image comes from the oxidized form of Cytochrome C oxidase. I circled the oxygen (O2) in the image so you can see where it is bound in the active site between the copper and the iron.
It turns out that certain poisons also bind in this location. And, we can use molecular models with or without those poisons as a learning activity.
The Molecular Murder Mysteries structure collection contains several samples of cytochrome C oxidase proteins collected, presumably, from victims at the murder scene. Students work with this collection in the Molecule World iPad app. They compare their assigned sample to the reduced and oxidized forms of cytochrome C oxidase in the collection to determine if their sample contains a poison, if it contains a poison, they use the color key identify the poison, then they come up with a story to explain how the victim was poisoned.
It's a great activity for Halloween!