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see coenzymecoenzyme
, any one of a group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the nonprotein component (the so-called prosthetic group) and the coloring matter of hemoglobin.

Chemically, heme is a compound of protoporphyrin and divalent iron. In the vertebrate body heme is synthesized from simpler nitrogen compounds (glycine and succinate) and from ferritin, a reserve iron-protein complex present in the spleen, liver, and bone marrow. The heme isolated from the blood of various vertebrates always has the same structure:

Free heme readily oxidizes in air to hematin, in which the iron atom is trivalent. Many years of research on the structure of heme were rewarded by the synthesis in 1929 by H. Fischer of hemin, the hydrochloride of heme.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


C34H32O4N4Fe An iron-protoporphyrin complex associated with each polypeptide unit of hemoglobin.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Green, "The effect of iron substrate on mitochondrial haem synthesis in copper deficiency," British Journal of Nutrition, vol.
Falcipain-II and falcipain-III are reported as haem degradation metabolizing enzymes responsible for initiating the degradation of host erythrocyte haemoglobin inside the food vacuole of the parasite.
There is strong evidence to suggest that the primary activator is an iron source, in the form of Fe2+, haem or both.
Other drugs are associated with porphyric crises, probably due to decreasing haem levels causing increased synthetic activity.
Methaemoglobin is produced physiologically, albeit at a low rate, when the electron originally donated by [Fe.sup 2+] to oxygen during oxygen carriage is not returned to the haem moiety upon deoxygenation.
This difference is due to the higher bioavailability of iron in the US diet mainly attributable to increased ascorbic acid content and haem iron consumption (16,34).
Unconjugated bilirubin is produced by the breakdown of haem, which is found in red blood cells.
Background: Acute Intermittent Porphyria (AIP) is a rare autosomal dominant metabolic disorder resulting from partial deficiency of porphobilinogen deaminase, the third enzyme of the haem synthetic pathway.
These iron deposits are the result of ineffective insertion of iron into the developing haem molecule.
When describing the iron present in food the terms haem and non-haem are used.
* Dietary iron exists in two forms: haem iron is found in foods from animal sources, especially meat; and non-haem iron is found mainly in plant foods.
Acquired methaemoglobinaemia may be secondary to accidental or intentional exposure to substances that carry the potential of increasing the rate of haem oxidation to the extent that it overwhelms the capacity of erythrocytes to maintain haemoglobin in the reduced state.