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. When carbon dioxide binds to hemoglobin, carbaminohemoglobin is formed, lowering hemoglobin's affinity for oxygen via the Haldane effect. In the absence of oxygen, unbound hemoglobin molecules have a greater chance of becoming carbaminohemoglobin. (The Bohr Effect relates to the increased affinity of de-oxygneated hemaglobin for H+: offloading of oxygen to the tissues thus results in increased affinity of the hemaglogin for carbon dioxide, and H+ - which the body wants to be rid of- which can then be transported to the lung for removal). The veins, which carry deoxygenated blood back to the right atrium of the heart appear bluish due to the distinctive blue color of carbaminohemoglobin.(The blue color of veinous blood is not related to oxygen levels which is the common perception). [1]
The nature of carbon dioxide's binding to hemoglobin to form carbaminohemoglobin is not always agreed upon by biochemistry texts. Four molecules of oxygen can bind to one molecule of hemoglobin. It is suggested by some that hemoglobin can also bind to four molecules of carbon dioxide. Among those who share this belief, it is generally agreed that each molecule of carbon dioxide must bind to a region on the heme monomer which a molecule of oxygen would not typically use. Other biochemistry texts claim that carbon dioxide does not bind to the hemoglobin tetramer at all and can only be found floating in the cytoplasm of the red blood cells. Research is currently being conducted in order to ascertain the truth of the matter. Haemoglobin contains the protein part called globin which combines with CO2.
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