This article's factual accuracy is disputed. Please help to ensure that disputed statements are reliably sourced. See the relevant discussion on the talk page.(December 2011)
Carbaminohemoglobin (or Carbaminohaemoglobin, also known as carbhaemoglobin and carbohaemoglobin) is a compound of haemoglobin and carbon dioxide, and is one of the forms in which carbon dioxide exists in the blood. 10% of carbon dioxide is carried in blood this way (85% carried in blood as bicarbonate (Hydrogen carbonate, 5% carried as free CO2, in solution).
When carbon dioxide binds to haemoglobin, carbaminohemoglobin is formed, lowering haemoglobin's affinity for oxygen via the Bohr effect. In the absence of oxygen, unbound haemoglobin molecules have a greater chance of becoming carbaminohaemoglobin. (The Haldane Effect relates to the increased affinity of de-oxygenated haemoglobin for H+: offloading of oxygen to the tissues thus results in increased affinity of the haemoglobin for carbon dioxide, and H+ - which the body wants to be rid of- which can then be transported to the lung for removal). Carbaminohemoglobin has a distinctive blue color that may contribute to the dark red color of deoxygenated venous blood (compared to bright, saturated red of oxygenated arterial blood), blue color of veins and the purplish or bluish color of tissues in hypoxia.
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 haemoglobin. It is suggested by some that haemoglobin 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 hememonomer which a molecule of oxygen would not typically use. Other biochemistry texts claim that carbon dioxide does not bind to the haemoglobin 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.