Magnesium-chelatase is a three-component enzyme (EC 6.6.1.1) that catalyses the insertion of Mg2+ into protoporphyrin IX.

[1][2] 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:

This enzyme belongs to the family of ligases, specifically those forming nitrogen-D-metal bonds in coordination complexes.

The systematic name of this enzyme class is Mg-protoporphyrin IX magnesium-lyase.

This enzyme is part of the biosynthetic pathway to chlorophylls.