Carbaminohemoglobin

Carbaminohemoglobin (or carbaminohaemoglobin, also known as carbhemoglobin and carbohemoglobin) is a compound of hemoglobin and carbon dioxide, and is one of the forms in which carbon dioxide exists in the blood. Twenty-three percent of carbon dioxide is carried in blood this way (70% is converted into bicarbonate by carbonic anhydrase and then carried in plasma, 7% carried as free CO2, in solution, or plasma).[1]

Mechanism

When carbon dioxide binds to hemoglobin, carbaminohemoglobin is formed, lowering hemoglobin's affinity for oxygen via the Bohr effect. The reaction is formed between a carbon dioxide molecule and an amino residue. [2]In the absence of oxygen, unbound hemoglobin molecules have a greater chance of becoming carbaminohemoglobin. The Haldane effect relates to the increased affinity of de-oxygenated hemoglobin for H+
: offloading of oxygen to the tissues thus results in increased affinity of the hemoglobin for carbon dioxide, and H+
, which the body wants to get rid of, which can then be transported to the lung for removal. Because the formation of this compound generates hydrogen ions, haemoglobin is needed to buffer it.[2]

Hemoglobin can bind to four molecules of carbon dioxide. The carbon dioxide molecules form a carbamate with the four terminal-amine groups of the four protein chains in the deoxy form of the molecule. Thus, one hemoglobin molecule can transport four carbon dioxide molecules back to the lungs, where they are released when the molecule changes back to the oxyhemoglobin form.

See also

References
  1. Gas Transport in the Blood FIG. 18.11 Carbon dioxide transport
  2. Waterhouse, James; Campbell, Iain (2005-11-01). "Respiration: gas transfer". Anaesthesia & Intensive Care Medicine. Thoracic. 6 (11): 363–366. doi:10.1383/anes.2005.6.11.363. ISSN 1472-0299.


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