Carbaminohemoglobin is formed when carbon dioxide binds to which molecule?

• A. Hemoglobin.
• B. Albumin.
• C. Hematocrit.
• D. Myoglobin.

Answer: (A)

Carbaminohemoglobin forms when carbon dioxide binds to hemoglobin. It attaches specifically to the amino groups on the globin protein part of hemoglobin (not to the heme iron), creating carbaminohemoglobin as the CO2 is carried from tissues back to the lungs. This binding helps transport CO2 and also influences oxygen release in tissues (the Bohr and Haldane effects). Most CO2 is carried as bicarbonate in plasma after hydration by carbonic anhydrase, but a portion binds directly to hemoglobin. Other molecules listed aren’t responsible for forming carbaminohemoglobin—albumin carries some CO2 in plasma, hematocrit is just a measure of red blood cell volume, and myoglobin is the muscle oxygen-binding protein.