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 carbon ...
macrocyclic metabolic intermediate in the
biosynthesis
Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...
of
sirohaem, the iron-containing prosthetic group in
sulfite reductase enzymes. It is also the
biosynthetic precursor to
cofactor F430, an enzyme which catalyzes the release of methane in the final step of
methanogenesis.
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 cosubstrate that binds to the enzyme apoenzyme (e ...
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 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 ...
and
hydroxymethylbilane to
uroporphyrinogen III. The latter is the first macrocyclic intermediate common to
haem,
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 ...
, sirohaem and
vitamin B12. Uroporphyrinogen III is subsequently transformed by the addition of two methyl groups to form
dihydrosirohydrochlorin and this is oxidised by
precorrin-2 dehydrogenase to give sirohydrochlorin.
See also
*
Sirohydrochlorin ferrochelatase an enzyme that catalyzes insertion of iron to form siroheme.
*
Sirohydrochlorin cobaltochelatase an enzyme that catalyzes insertion of cobalt.
References
{{Tetrapyrroles
Tetrapyrroles