Mechanism of the Mg-chelatase step in chlorophyll biosynthesis. Final technical report

Mg-chelatase catalyzes the insertion of Mg2+ into protoporphyrin-IX (Proto) in the chlorophyll biosynthetic pathway. This is the first step unique to the chlorophyll pathway and is at the branchpoint between heme and chlorophyll biosynthesis. Previous work from our laboratory has shown that the enzyme from pea chloroplasts requires three distinct protein fractions (now known to contain the D, I and H subunits). The reaction requires ATP in two distinct steps: activation requiring two of the fractions (I and D) and metal ion insertion, requiring all three fractions. Work covered in this granting period includes the cloning and expression of the active form of one of the pea subunits and demonstration of the change in chromatographic behavior of the subunits upon activation with ATP