Which pigment binds oxygen in some invertebrates using iron?

Which pigment binds oxygen in some invertebrates using iron?

• A. Hemerythrin
• B. Hemocyanin
• C. Hemoglobin
• D. Myoglobin

Answer: (A)

Oxygen transport in some invertebrates uses iron in a form different from the familiar heme-based pigments. Hemerythrin binds oxygen with a diiron center that is not part of a heme group. This iron-centered site reversibly captures O2, and the protein is typically soluble in the hemolymph rather than housed in red blood cells. When oxygen binds, the complex changes color—from colorless in the deoxygenated state to pinkish or violet in the oxygenated state—reflecting the electronic changes at the iron center. This distinguishes it from hemocyanin, which uses copper and is blue when bound to O2, and from hemoglobin and myoglobin, which rely on heme-bound iron. So the pigment that uses iron in some invertebrates to bind oxygen is hemerythrin.

Oxygen transport in some invertebrates uses iron in a form different from the familiar heme-based pigments. Hemerythrin binds oxygen with a diiron center that is not part of a heme group. This iron-centered site reversibly captures O2, and the protein is typically soluble in the hemolymph rather than housed in red blood cells. When oxygen binds, the complex changes color—from colorless in the deoxygenated state to pinkish or violet in the oxygenated state—reflecting the electronic changes at the iron center. This distinguishes it from hemocyanin, which uses copper and is blue when bound to O2, and from hemoglobin and myoglobin, which rely on heme-bound iron. So the pigment that uses iron in some invertebrates to bind oxygen is hemerythrin.