Sirohydrochlorin is a

tetrapyrrole Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four car ...

macrocyclic 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. ...

metabolic intermediate Metabolic intermediates are molecules that are the precursors or metabolites of biologically significant molecules. Although these intermediates are of relatively minor direct importance to cellular function, they can play important roles in the a ...

in the

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

sirohaem Siroheme (or sirohaem) is a heme-like prosthetic group at the active sites of some enzymes to accomplish the six-electron reduction of sulfur and nitrogen. It is a cofactor at the active site of sulfite reductase, which plays a major role in su ...

, the iron-containing prosthetic group in sulfite reductase enzymes. It is also the biosynthetic precursor to

cofactor F430 F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR). MCR catalyzes the reaction that releases methane in the final step of methanogenesis: : + HS–CoB → + CoB–S–S–CoM It is found ...

, an enzyme which catalyzes the release of methane in the final step of

methanogenesis Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group ...

Structure

Sirohydrochlorin was first isolated in the early 1970s when it was shown to be the metal-free form of the

prosthetic group A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being tightly linked to the apoprotein. Not to be confused with the cofactor that binds to the enzyme apoenzyme (eith ...

in the ferredoxin-nitrite reductase from spinach. Its chemical identity was established by spectroscopy and by total synthesis.

Biosynthesis

Sirohydrochlorin is derived from a tetrapyrrolic structural framework created by the enzymes

deaminase Deamination is the removal of an amino group from a molecule. Enzymes that catalyse this reaction are called deaminases. In the human body, deamination takes place primarily in the liver, however it can also occur in the kidney. In situations of ...

and cosynthetase which transform aminolevulinic acid via

porphobilinogen 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 a ...

and

hydroxymethylbilane Hydroxymethylbilane, also known as preuroporphyrinogen, is an organic compound that occurs in living organisms during the synthesis of porphyrins, a group of critical substances that include haemoglobin, myoglobin, and chlorophyll. The name is ofte ...

uroporphyrinogen III Uroporphyrinogen III is a tetrapyrrole, the first 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 uroporphyri ...

. The latter is the first macrocyclic intermediate common to

haem Heme, or haem (pronounced /Help:IPA/English, hi:m/ ), is a precursor (chemistry), precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, ...

chlorophyll Chlorophyll (also chlorophyl) 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 allow plants to a ...

, sirohaem and vitamin B₁₂. Uroporphyrinogen III is subsequently transformed by the addition of two methyl groups to form

dihydrosirohydrochlorin Dihydrosirohydrochlorin is one of several naturally occurring tetrapyrrole macrocyclic metabolic intermediates in the biosynthesis of vitamin B12 (cobalamin). Its oxidised form, sirohydrochlorin, is precursor to sirohaem, the iron-containing pr ...

and this is oxidised to give sirohydrochlorin.

References

{{Tetrapyrroles Tetrapyrroles

Structure

Biosynthesis

See also

References