Carbaminohemoglobin (carbaminohaemoglobin

BrE British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadly, ...

) (CO₂Hb, also known as carbhemoglobin and carbohemoglobin) is a

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...

and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

, and is one of the forms in which carbon dioxide exists in the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

. Twenty-three percent of carbon dioxide is carried in

this way (70% is converted into

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochem ...

by carbonic anhydrase and then carried in plasma, 7% carried as free CO₂, dissolved in plasma).

Synthesis

When the tissues release carbon dioxide into the bloodstream, around 10% is dissolved into the plasma. The rest of the carbon dioxide is carried either directly or indirectly by

. Approximately 10% of the carbon dioxide carried by hemoglobin is in the form of carbaminohemoglobin. This carbaminohemoglobin is formed by the reaction between carbon dioxide and an amino (-NH₂) residue from the globin molecule, resulting in the formation of a carbamino residue (-NH.COO⁻). The rest of the carbon dioxide is transported in the plasma as bicarbonate anions.

Mechanism

When carbon dioxide binds to hemoglobin, carbaminohemoglobin is formed, lowering hemoglobin's affinity for

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

via the Bohr effect. The reaction is formed between a carbon dioxide molecule and an amino residue. In the absence of oxygen, unbound hemoglobin molecules have a greater chance of becoming carbaminohemoglobin. The

Haldane effect The Haldane effect is a property of hemoglobin first described by John Scott Haldane, within which oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of carbon dioxide. Consequently, oxygenated blood ...

relates to the increased affinity of de-oxygenated hemoglobin for : offloading of oxygen to the tissues thus results in increased affinity of the hemoglobin for

, and , which the body needs 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. 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.

Hydrogen Ion and Oxygen-Carbon Dioxide Coupling

When carbon dioxide diffuses as a dissolved gas from the tissue capillaries, it binds to the α-amino terminus of the globulin chain, forming Carbaminohemoglobin. Carbaminohemoglobin is able to directly stabilise the T conformation as part of the carbon dioxide Bohr effect. Deoxyhemoglobin in turn subsequently increases the uptake of carbon dioxide in the form of favouring the formation of Bicarbonate as well as Carbaminohemoglobin through the

References

External links

* Biomolecules Hemoglobins {{protein-stub

Synthesis

Mechanism

Hydrogen Ion and Oxygen-Carbon Dioxide Coupling

See also

References

External links