chelatase

Chelatases are enzymes that catalyze the chelation, or insertion, of a metal ion into a macrocyclic ligand, most commonly a tetrapyrrole such as a porphyrin or corrin. These reactions are essential in the biosynthesis of key cofactors, including heme, chlorophyll, and cobalamin (vitamin B12).

Ferrochelatase is the enzyme that inserts iron(II) into protoporphyrin IX to form heme. In eukaryotes, ferrochelatase is located in the inner mitochondrial membrane, while in many bacteria it functions in the cytosol. It is a terminal enzyme in the heme biosynthesis pathway, and defects in ferrochelatase can lead to disorders such as erythropoietic protoporphyria in humans.

Magnesium chelatase catalyzes the insertion of magnesium(II) into protoporphyrin IX to produce magnesium protoporphyrin IX, the first committed step toward chlorophyll biosynthesis. This reaction is ATP-dependent and is carried out by a multi-subunit complex (for example CHLI/CHLD/CHLH in plants and BchI/BchD/BchH in bacteria). The enzyme is localized to plastids in plants and cyanobacterial photosynthetic membranes in prokaryotes.

Cobalt and other metal chelatases participate in the biosynthesis of cobalamin (vitamin B12) by inserting cobalt into sirohydrochlorin, a step performed by cobalt chelatase enzymes such as CobN or CbiK in bacteria. These enzymes often function within larger operons or complexes and may also require auxiliary proteins.

Chelatases are broadly distributed across bacteria, archaea, and eukaryotes, reflecting their central role in metal insertion into biologically important tetrapyrrole or related macrocycles.