(Minus) S-adenosyl-L-methionine-magnesium protoporphyrin methyltransferase, an enzyme in the biosynthetic pathway of chlorophyll in Zea mays.

The enzyme (-) S-adenosyl-L-methionine-magnesium protoporphyrin methyltransferase, which catalyzes the transfer of the methyl group from (-) S-adenosyl-L-methionine to magnesium protoporphyrin to form magnesium protoporphyrin monomethyl ester, has been detected in chloroplasts isolated from Zea mays. Zinc protoporphyrin and free protoporphyrin also act as substrates in the system, although neither one is as active as magnesium protoporphyrin. THE FOLLOWING SCHEME OF CHLOROPHYLL SYNTHESIS IN HIGHER PLANTS IS PROPOSED: delta-aminolevulinic acid --> --> --> protoporphyrin --> magnesium protoporphyrin --> magnesium protoporphyrin monomethyl ester --> --> --> chlorophyll a.