When carbon monoxide binds to haemoglobin, which compound is formed?

When carbon monoxide binds to haemoglobin, which compound is formed?

• A. Carboxyhaemoglobin
• B. Met haemoglobin
• C. Oxyhaemoglobin
• D. Deoxyhaemoglobin

Answer: (A)

When carbon monoxide binds to haemoglobin, it forms carboxyhaemoglobin. CO attaches to the iron in the heme group with a much higher affinity than oxygen, so it rapidly outcompetes O2 for binding sites. This not only decreases the amount of oxygen that can be carried, but also shifts the oxygen dissociation curve to the left, making haemoglobin hold onto any remaining oxygen more tightly and release less to tissues. The result is tissue hypoxia even if oxygen levels are normal. For context, methemoglobin is iron in the ferric state and cannot bind O2; oxyhaemoglobin is haemoglobin bound to O2; deoxyhaemoglobin is haemoglobin not bound to O2.

When carbon monoxide binds to haemoglobin, it forms carboxyhaemoglobin. CO attaches to the iron in the heme group with a much higher affinity than oxygen, so it rapidly outcompetes O2 for binding sites. This not only decreases the amount of oxygen that can be carried, but also shifts the oxygen dissociation curve to the left, making haemoglobin hold onto any remaining oxygen more tightly and release less to tissues. The result is tissue hypoxia even if oxygen levels are normal. For context, methemoglobin is iron in the ferric state and cannot bind O2; oxyhaemoglobin is haemoglobin bound to O2; deoxyhaemoglobin is haemoglobin not bound to O2.