What is the structural difference between hemerythrin and hemocyanin in terms of metal usage?

What is the structural difference between hemerythrin and hemocyanin in terms of metal usage?

• A. Hemerythrin uses iron; hemocyanin uses copper
• B. Hemerythrin uses copper; hemocyanin uses iron
• C. Both use iron but differ in oxygen-binding site
• D. Hemerythrin uses zinc; hemocyanin uses copper

Answer: (A)

The important idea is that these two oxygen-carrying proteins differ in the metal they use to bind oxygen. Hemerythrin carries oxygen with a non-heme iron center, consisting of two iron atoms coordinated by surrounding amino acids. Oxygen binds across those two iron atoms, and the iron atoms cycle between oxidation states during binding and release. Hemocyanin, on the other hand, uses copper at a dicopper center. Oxygen binds across the two copper ions in a cooperative way, forming a dicopper-oxygen complex. So the structural difference is that one protein relies on iron (not iron in a heme group but a diiron site) while the other relies on copper at a dicopper site. The other options aren’t correct because hemerythrin does not use copper, hemocyanin does not use iron, and zinc is not involved in these oxygen-transport proteins.

The important idea is that these two oxygen-carrying proteins differ in the metal they use to bind oxygen. Hemerythrin carries oxygen with a non-heme iron center, consisting of two iron atoms coordinated by surrounding amino acids. Oxygen binds across those two iron atoms, and the iron atoms cycle between oxidation states during binding and release. Hemocyanin, on the other hand, uses copper at a dicopper center. Oxygen binds across the two copper ions in a cooperative way, forming a dicopper-oxygen complex.

So the structural difference is that one protein relies on iron (not iron in a heme group but a diiron site) while the other relies on copper at a dicopper site. The other options aren’t correct because hemerythrin does not use copper, hemocyanin does not use iron, and zinc is not involved in these oxygen-transport proteins.