Carbaminohemoglobine

Carbaminohemoglobine, or carbaminohemoglobin, is the reversible form of hemoglobin bound to carbon dioxide. It represents one of the ways carbon dioxide is transported in the blood. In humans, about 5–10% of total CO2 is carried as carbaminohemoglobin, with the remainder primarily in the form of bicarbonate in plasma and dissolved CO2.

Formation and mechanism: CO2 diffuses from tissues into red blood cells, where carbonic anhydrase rapidly converts much of it to bicarbonate and protons. A portion of CO2 also binds directly to the amino groups at the N-termini of the globin chains, forming carbaminohemoglobin (Hb-CO2). This binding is favored when hemoglobin is in the deoxygenated state. The formation of carbaminohemoglobin releases protons, contributing to the Bohr effect, which promotes oxygen unloading in tissues.

Physiological role: Carbaminohemoglobin participates in CO2 transport from tissues to the lungs. The binding of CO2 to deoxygenated Hb facilitates CO2 uptake in tissues, while in the lungs, oxygenation promotes release of CO2 from Hb. This exchange is linked to the Haldane effect, wherein deoxygenation enhances CO2 binding and oxygenation promotes CO2 release.

Sites and reversibility: The carbamate groups form at the N-terminal amino groups of the globin chains, mainly on the beta chains. The Hb-CO2 bond is reversible, allowing CO2 to be released in the lungs for exhalation.

Clinical and physiological notes: The relative contribution of carbaminohemoglobin to CO2 transport can be influenced by factors such as blood pH, temperature, and the level of hemoglobin oxygenation.