Magnesium-protoporphyrin IX monomethyl ester (oxidative) cyclase

In green tissue, ferredoxin can receive these electrons directly from photosystem I so that NADPH need not be involved.

However, in the dark, ferredoxin can also be reduced via Ferredoxin—NADP(+) reductase, allowing the reaction to proceed in that case.

It is therefore more accurate to show the individual steps as follows: This enzyme requires Fe(II) for activity.

An associated protein, Ycf54, seems to be required for proper maturation of the XanL enzyme,[2] which is part of the biosynthetic pathway to chlorophylls.

[3][4][5] In anaerobic organisms such as Rhodobacter sphaeroides the same overall transformation occurs but the oxygen incorporated into magnesium-protoporphyrin IX 13-monomethyl ester comes from water in the reaction EC 1.21.98.3.