Magnesium-chelatase is a three-component enzyme that catalyses the insertion of Mg<sup>2+</sup> into protoporphyrin IX. This is the first unique step in the synthesis of (bacterio)chlorophyll. As a result, it is thought that Mg-chelatase has an important role in channeling intermediates into the (bacterio)chlorophyll branch in response to conditions suitable for photosynthetic growth. ChlI and BchD have molecular weights between 38-42 kDa.