Carbaminohemoglobin forms when which substance binds to haemoglobin?

• A. Binding of carbon dioxide to amino groups of haemoglobin
• B. Binding of carbon monoxide to haemoglobin
• C. Binding of oxygen to haemoglobin
• D. Binding of nitrogen to haemoglobin

Answer: (A)

Carbon dioxide forms carbaminohemoglobin by attaching to the amino groups on the globin part of the hemoglobin molecule, specifically at the N-termini of the protein chains. This creates a carbamino compound that helps transport CO2 from tissues back to the lungs. It’s different from carboxyhemoglobin, where carbon monoxide binds to the heme iron, and from oxygen binding, which also attaches to the heme iron. Nitrogen does not bind hemoglobin in this way. This CO2 binding is favored when hemoglobin is deoxygenated, which is part of how CO2 is carried from tissues to the lungs.