Global InformationHemoglobin information
| Hemoglobin | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (heterotetramer, (αβ)2) | |||||||||||||
 Structure of human hemoglobin. α and β globin subunits are in red and blue, respectively, and the iron-containing heme groups in green. From PDB: 1GZX Proteopedia Hemoglobin | |||||||||||||
| Protein type | metalloprotein, chromoprotein, globulin | ||||||||||||
| Function | oxygen-transport | ||||||||||||
| Cofactor(s) | heme (4) | ||||||||||||
| |||||||||||||
Hemoglobin (haemoglobin,[a] Hb or Hgb) is a protein containing iron that facilitates the transport of oxygen in red blood cells. Almost all vertebrates contain hemoglobin,[3] with the exception of the fish family Channichthyidae.[4] Hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the other tissues of the body, where it releases the oxygen to enable aerobic respiration which powers the animal's metabolism. A healthy human has 12 to 20 grams of hemoglobin in every 100 mL of blood. Hemoglobin is a metalloprotein, a chromoprotein, and globulin.
In mammals, hemoglobin makes up about 96% of a red blood cell's dry weight (excluding water), and around 35% of the total weight (including water).[5] Hemoglobin has an oxygen-binding capacity of 1.34 mL of O2 per gram,[6] which increases the total blood oxygen capacity seventy-fold compared to dissolved oxygen in blood plasma alone.[7] The mammalian hemoglobin molecule can bind and transport up to four oxygen molecules.[8]
Hemoglobin also transports other gases. It carries off some of the body's respiratory carbon dioxide (about 20–25% of the total)[9] as carbaminohemoglobin, in which CO2 binds to the heme protein. The molecule also carries the important regulatory molecule nitric oxide bound to a thiol group in the globin protein, releasing it at the same time as oxygen.[10]
Hemoglobin is also found in other cells, including in the A9 dopaminergic neurons of the substantia nigra, macrophages, alveolar cells, lungs, retinal pigment epithelium, hepatocytes, mesangial cells of the kidney, endometrial cells, cervical cells, and vaginal epithelial cells.[11] In these tissues, hemoglobin absorbs unneeded oxygen as an antioxidant, and regulates iron metabolism.[12] Excessive glucose in the blood can attach to hemoglobin and raise the level of hemoglobin A1c.[13]
Hemoglobin and hemoglobin-like molecules are also found in many invertebrates, fungi, and plants.[14] In these organisms, hemoglobins may carry oxygen, or they may transport and regulate other small molecules and ions such as carbon dioxide, nitric oxide, hydrogen sulfide and sulfide. A variant called leghemoglobin serves to scavenge oxygen away from anaerobic systems such as the nitrogen-fixing nodules of leguminous plants, preventing oxygen poisoning.
The medical condition hemoglobinemia, a form of anemia, is caused by intravascular hemolysis, in which hemoglobin leaks from red blood cells into the blood plasma.
- ^ Wells, John C. (2008). Longman Pronunciation Dictionary (3rd ed.). Longman. ISBN 978-1-4058-8118-0.
- ^ Jones, Daniel (2011). Roach, Peter; Setter, Jane; Esling, John (eds.). Cambridge English Pronouncing Dictionary (18th ed.). Cambridge University Press. ISBN 978-0-521-15255-6.
- ^ Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, US: Prentice Hall. ISBN 978-0-13-981176-0.
- ^ Sidell, Bruce; Kristin O'Brien (2006). "When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes". The Journal of Experimental Biology. 209 (Pt 10): 1791–802. doi:10.1242/jeb.02091. PMID 16651546. S2CID 29978182.
- ^ Weed, Robert I.; Reed, Claude F.; Berg, George (1963). "Is hemoglobin an essential structural component of human erythrocyte membranes?". J Clin Invest. 42 (4): 581–88. doi:10.1172/JCI104747. PMC 289318. PMID 13999462.
- ^ Dominguez de Villota ED, Ruiz Carmona MT, Rubio JJ, de Andrés S (1981). "Equality of the in vivo and in vitro oxygen-binding capacity of hemoglobin in patients with severe respiratory disease". Br J Anaesth. 53 (12): 1325–28. doi:10.1093/bja/53.12.1325. PMID 7317251. S2CID 10029560.
- ^ Rhodes, Carl E.; Denault, Deanna; Varacallo, Matthew (2023), "Physiology, Oxygen Transport", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30855920, retrieved 2023-04-15
- ^ Costanzo, Linda S. (2007). Physiology. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 978-0-7817-7311-9.
- ^ Patton, Kevin T. (2015-02-10). Anatomy and Physiology. Elsevier Health Sciences. ISBN 978-0-323-31687-3. Archived from the original on 2016-04-26. Retrieved 2016-01-09.
- ^ Epstein, F. H.; Hsia, C. C. W. (1998). "Respiratory Function of Hemoglobin". New England Journal of Medicine. 338 (4): 239–47. doi:10.1056/NEJM199801223380407. PMID 9435331.
- ^ Saha, D.; Reddy, K. V. R.; Patgaonkar, M.; Ayyar, K.; Bashir, T.; Shroff, A. (2014). "Hemoglobin Expression in Nonerythroid Cells: Novel or Ubiquitous?". International Journal of Inflammation. 2014 (803237): 1–8. doi:10.1155/2014/803237. PMC 4241286. PMID 25431740.
- ^ Biagioli M, Pinto M, Cesselli D, et al. (2009). "Unexpected expression of alpha- and beta-globin in mesencephalic dopaminergic neurons and glial cells". Proceedings of the National Academy of Sciences of the United States of America. 106 (36): 15454–59. Bibcode:2009PNAS..10615454B. doi:10.1073/pnas.0813216106. PMC 2732704. PMID 19717439.
- ^ "Blood Tests". National Heart, Lung, and Blood Institute (NHLBI). Archived from the original on 2019-04-09. Retrieved 2019-04-27.
- ^ Cite error: The named reference
Weber-2001was invoked but never defined (see the help page).
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