Sirohydrochlorin Explained

Sirohydrochlorin is a tetrapyrrole macrocyclic metabolic intermediate in the biosynthesis 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.^[1]

Structure

Sirohydrochlorin was first isolated in the early 1970s when it was shown to be the metal-free form of the prosthetic group in the ferredoxin-nitrite reductase from spinach.^[2] Its chemical identity was established by spectroscopy and by total synthesis.^{[3] [4] [5]}

Biosynthesis

Sirohydrochlorin is derived from a tetrapyrrolic structural framework created by the enzymes deaminase and cosynthetase which transform aminolevulinic acid via porphobilinogen and hydroxymethylbilane to uroporphyrinogen III. The latter is the first macrocyclic intermediate common to haem, chlorophyll, 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.^[6]

See also

• Sirohydrochlorin ferrochelatase an enzyme that catalyzes insertion of iron to form siroheme.
• Sirohydrochlorin cobaltochelatase an enzyme that catalyzes insertion of cobalt.

Notes and References

1. Mucha. Helmut. Keller. Eberhard. Weber. Hans. Lingens. Franz. Trösch. Walter. 1985-10-07. Sirohydrochlorin, a precursor of factor F430 biosynthesis in Methanobacterium thermoautotrophicum. FEBS Letters. 190. 1. 169–171. 10.1016/0014-5793(85)80451-8. free.
2. 10.1073/pnas.71.3.612 . Siroheme: A New Prosthetic Group Participating in Six-Electron Reduction Reactions Catalyzed by Both Sulfite and Nitrite Reductases . 1974 . Murphy . M. J. . Siegel . L. M. . Tove . S. R. . Kamin . H. . Proceedings of the National Academy of Sciences . 71 . 3 . 612–616 . 4595566 . 388061 . 1974PNAS...71..612M . free .
3. 10.1021/ja00493a031 . Sirohydrochlorin. Prosthetic group of sulfite and nitrite reductases and its role in the biosynthesis of vitamin B12 . 1978 . Scott . A. Ian . Irwin . Anthony J. . Siegel . Lewis M. . Shoolery . J. N. . Journal of the American Chemical Society . 100 . 25 . 7987–7994 .
4. 10.1039/C39780000150 . Biosynthesis of vitamin B12: Proof of A-B structure for sirohydrochlorin by its specific incorporation into cobyrinic acid . 1978 . Battersby . Alan R. . McDonald . Edward . Thompson . Mervyn . Bykhovsky . Vladimir Ya. . Journal of the Chemical Society, Chemical Communications . 3 . 150 .
5. 10.1039/C39850001061 . Syntheses relevant to vitamin B12 biosynthesis: Synthesis of sirohydrochlorin and of its octamethyl ester . 1985 . Block . Michael H. . Zimmerman . Steven C. . Henderson . Graeme B. . Turner . Simon P. D. . Westwood . Steven W. . Leeper . Finian J. . Battersby . Alan R. . Journal of the Chemical Society, Chemical Communications . 16 . 1061 .
6. 10.1039/B002635M . Tetrapyrroles: The pigments of life: A Millennium review . 2000 . Battersby . Alan R. . Natural Product Reports . 17 . 6 . 507–526 . 11152419 .