Hydroxymethyl Bilane on:
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Hydroxymethylbilane, also known as preuroporphyrinogen, is an
The enzyme uroporphyrinogen III synthase closes the chain to form 
Uroporphyrinogen III is a
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
that occurs in living organisms during the synthesis of porphyrin
Porphyrins ( ) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (). In vertebrates, an essential member of the porphyrin group is heme, w ...
s, a group of critical substances that include haemoglobin
Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobi ...
, myoglobin
Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle, skeletal Muscle, muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compar ...
, and chlorophyll
Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...
. The name is often abbreviated as HMB.
Structure
The compound is a substitutedbilane
In organic chemistry, bilane is a compound with the formula or . It is a tetrapyrrole, a class of compounds with four independent pyrrole rings. Specifically, the molecule can be described as four pyrrole molecules connected in an open chain by ...
, a chain of four pyrrole
Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrol ...
rings interconnected by methylene bridge
In chemistry, a methylene bridge is part of a molecule with formula . The carbon atom is connected by single bonds to two other distinct atoms in the rest of the molecule. A methylene bridge is often called a methylene group or simply methylene, ...
s . The chain starts with a hydroxymethyl
The hydroxymethyl group is a substituent with the structural formula . It consists of a methylene bridge ( unit) bonded to a hydroxyl group (). This makes the hydroxymethyl group an alcohol. It has the identical chemical formula with the methoxy g ...
group and ends with a hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
, in place of the respective methylene bridges. The other two carbon atoms of each pyrrole cycle are connected to an acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
group and a propionic acid
Propionic acid (, from the Greek language, Greek words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula . It is a ...
group , in that order.
Metabolism
HMB is generated from four molecules ofporphobilinogen
Porphobilinogen (PBG) is an organic compound that occurs in living organisms as an intermediate in the biosynthesis of porphyrins, which include critical substances like hemoglobin and chlorophyll.
The structure of the molecule can be described ...
by the enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
porphobilinogen deaminase
Porphobilinogen deaminase (hydroxymethylbilane synthase, or uroporphyrinogen I synthase) is an enzyme () that in humans is encoded by the HMBS gene. Porphobilinogen deaminase is involved in the third step of the heme biosynthetic pathway. It catal ...
:
The enzyme uroporphyrinogen III synthase closes the chain to form uroporphyrinogen III
Uroporphyrinogen III is a tetrapyrrole, the first macrocycle, macrocyclic intermediate in the biosynthesis of heme, chlorophyll, vitamin B12, and siroheme. It is a colorless compound, like other porphyrinogens.
Structure
The molecular structure of ...
:
Uroporphyrinogen III is a porphyrinogen
In biochemistry, a porphyrinogen is a member of a class of naturally occurring compounds with a tetrapyrrole core, a macrocycle of four pyrrole rings connected by four methylene bridges.
, which is a class of compounds with the hexahydroporphine macrocycle
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. ...
. In the absence of the enzyme, the compound undergoes spontaneous cyclization and becomes uroporphyrinogen I.
References
{{Heme metabolism intermediates Tetrapyrroles Carboxylic acids