What is oxyhemoglobin?

• A. Hemoglobin bound to four molecules of oxygen
• B. Hemoglobin bound to carbon monoxide
• C. Hemoglobin bound to carbon dioxide
• D. Hemoglobin bound to hydrogen ions

Answer: (A)

Oxyhemoglobin is the form of hemoglobin with oxygen bound to it. Hemoglobin has four heme groups, each with an iron ion that can bind one O2 molecule, so the molecule can carry up to four oxygen molecules. This binding happens most readily in the lungs, where oxygen concentration is high, and the oxygen is released in tissues where it’s needed. Oxyhemoglobin is the bright red form of Hb, reflecting its oxygenated state.

Other bindings describe different ligands: carbon monoxide binds to hemoglobin to form carboxyhemoglobin, carbon dioxide binds to amino groups to form carbaminohemoglobin, and hydrogen ions influence oxygen release via the Bohr effect but aren’t what oxyhemoglobin is.