Editing Bohr effect (section)

=== Carbon monoxide ===
Another special case of the Bohr effect occurs when [[carbon monoxide]] is present. This molecule serves as a [[Competitive inhibition|competitive inhibitor]] for oxygen, and binds to haemoglobin to form [[carboxyhemoglobin|carboxyhaemoglobin]].<ref name=":4" /> Haemoglobin's affinity for CO is about 210 times stronger than its affinity for O<sub>2</sub>,<ref>{{Cite book|title=Guyton and Hall Textbook of Medical Physiology (12th ed.)|last=Hall|first=John E.|publisher=Saunders/Elsevier|year=2010|isbn=978-1416045748|location=Philadelphia, Pa|pages=502}}</ref> meaning that it is very unlikely to dissociate, and once bound, it blocks the binding of O<sub>2</sub> to that subunit. At the same time, CO is structurally similar enough to O<sub>2</sub> to cause carboxyhemoglobin to favor the R state, raising the oxygen affinity of the remaining unoccupied subunits. This combination significantly reduces the delivery of oxygen to the tissues of the body, which is what makes carbon monoxide so [[Carbon monoxide poisoning|toxic]]. This toxicity is reduced slightly by an increase in the strength of the Bohr effect in the presence of carboxyhemoglobin. This increase is ultimately due to differences in interactions between heme groups in carboxyhemoglobin relative to oxygenated hemoglobin. It is most pronounced when the oxygen concentration is extremely low, as a last-ditch effort when the need for oxygen delivery becomes critical. However, the physiological implications of this phenomenon remain unclear.<ref name=":4">{{Cite journal|last1=Hlastala|first1=M. P.|last2=McKenna|first2=H. P.|last3=Franada|first3=R. L.|last4=Detter|first4=J. C.|date=1976-12-01|title=Influence of carbon monoxide on hemoglobin-oxygen binding|journal=Journal of Applied Physiology|volume=41|issue=6|pages=893–899|issn=0021-8987|pmid=12132|doi=10.1152/jappl.1976.41.6.893}}</ref>