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] 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.

[3][4][5] 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.

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.