IUBMB Enzyme Nomenclature


Accepted name: sirohydrochlorin cobaltochelatase

Reaction: cobalt-sirohydrochlorin + 2 H+ = sirohydrochlorin + Co2+

For diagram click here.

Other name(s): CbiK; CbiX; CbiXS; anaerobic cobalt chelatase; cobaltochelatase [ambiguous]; sirohydrochlorin cobalt-lyase (incorrect)

Systematic name: cobalt-sirohydrochlorin cobalt-lyase (sirohydrochlorin-forming)

Comments: This enzyme is a type II chelatase, being either a monomer (CbiX) or a homodimer (CibK) and being ATP-independent. CbiK from Salmonella enterica uses precorrin-2 as the substrate to yield cobalt-precorrin-2. The enzyme contains two histidines at the active site that are thought to be involved in the deprotonation of the tetrapyrrole substrate as well as in metal binding. CbiX from Bacillus megaterium inserts cobalt at the level of sirohydrochlorin (factor-II) rather than precorrin-2.

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:


1. Schubert, H.L., Raux, E., Wilson, K.S. and Warren, M.J. Common chelatase design in the branched tetrapyrrole pathways of heme and anaerobic cobalamin synthesis. Biochemistry 38 (1999) 10660-10669. [PMID: 10451360]

2. Brindley, A.A., Raux E., Leech, H.K., Schubert, H.L. and Warren, M.J. A story of chelatase evolution: Identification and characterisation of a small 13-15 kDa 'ancestral' cobaltochelatase (CbiXS) in the Archaea. J. Biol. Chem. 278 (2003) 22388-22395. [PMID: 12686546]

3. Warren, M.J., Raux, E., Schubert, H.L. and Escalante-Semerena, J.C. The biosynthesis of adenosylcobalamin (vitamin B12). Nat. Prod. Rep. 19 (2002) 390-412. [PMID: 12195810]

[EC created 2004]

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