Chelatase

 ( Ligases ) 

In biochemistry, chelatases are that catalyze the insertion ("metalation") of naturally occurring . Many tetrapyrrole-based cofactors exist in nature including , , and vitamin B12. These metallo cofactors are derived by the reaction of metal cations with tetrapyrroles, which are not per se, but the conjugate acids thereof. In the case of , the reaction that chelatases catalyze is:

Fe²⁺ + H₂P → FeP + 2 H⁺

In the above equation H₂P represents a sirohydrochlorin or a porphyrin, such as protoporphyrin IX.

Chelatases are required because porphyrins and related macrocyclic ligands are extremely slow to metalate, despite favorable thermodynamics. These low rates are attributed to the tight fit of the metal into the rigid 18- or 17-membered tetrapyrrole macrocycle. Several families of chelatase are known including cobalt chelatase, magnesium chelatase, and ferrochelatase. Nickel insertion into a sirohydrochlorin also requires a chelatase as part of the biosynthesis of cofactor F430. Apparently that chelatase is identical to the cobalt chelatase.

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