Magnesium chelatase: Mg-chelatase catalyses the insertion of Mg into protoporphyrin IX (Proto). In chlorophyll biosynthesis, insertion of Mg2+ into protoporphyrin IX is catalysed by magnesium chelatase in an ATP-dependent reaction. Magnesium chelatase is a three sub-unit (BchI, BchD and BchH) enzyme with a novel arrangement of domains: the C-terminal helical domain is located behind the nucleotide binding site. The BchD domain contains a AAA domain at its N-terminus and a VWA domain at its C-terminus. The VWA domain has been speculated to be involved in mediating protein-protein interactions.