Sirohydrochlorin ferrochelatase

In enzymology, a sirohydrochlorin ferrochelatase (EC4.99.1.4) is an enzyme that catalyzes the chemical reaction

Thus, the two substrates of this enzyme are sirohydrochlorin and Fe2, whereas its two products are sirohaem and H.

This enzyme belongs to the family of lyases, to be specific the "catch-all" class of lyases that do not fit into any other sub-class. The systematic name of this enzyme class is siroheme ferro-lyase (sirohydrochlorin-forming). The enzyme is also known as SirB and present in all plants and nitrate and sulfate assimilating/dissimilating bacteria. Siroheme is a co-factor of both assimilatory and dissimilatory nitrite and sulfite reductases. Siroheme is synthesized from the central tetrapyrrole molecule uroporphyrinogen III, which forms the first branch-point of tetrapyrrole biosynthetic pathway, the other branch being the heme/chlorophyll branch. The siroheme branch consists of three steps, methylation, dehydrogenation and ferrochelation, with the last step carried out by sirohydrochlorin ferrochelatase.