IUBMB Enzyme Nomenclature


Accepted name: magnesium-protoporphyrin IX monomethyl ester (oxidative) cyclase

Reaction: magnesium-protoporphyrin IX 13-monomethyl ester + 3 NADPH + 3 H+ + 3 O2 = 3,8-divinyl protochlorophyllide a + 3 NADP+ + 5 H2O (overall reaction)
(1a) magnesium-protoporphyrin IX 13-monomethyl ester + NADPH + H+ + O2 = 131-hydroxy-magnesium-protoporphyrin IX 13-monomethyl ester + NADP+ + H2O
(1b) 131-hydroxy-magnesium-protoporphyrin IX 13-monomethyl ester + NADPH + H+ + O2 = 131-oxo-magnesium-protoporphyrin IX 13-monomethyl ester + NADP+ + 2 H2O
(1c) 131-oxo-magnesium-protoporphyrin IX 13-monomethyl ester + NADPH + H+ + O2 = 3,8-divinyl protochlorophyllide a + NADP+ + 2 H2O

For diagram of reaction click here.

Other name(s): Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase

Systematic name: magnesium-protoporphyrin-IX 13-monomethyl ester,NADPH:oxygen oxidoreductase (hydroxylating)

Comments: Requires iron((II) for activity. The enzyme participates in the biosynthesis of chlorophyllide a in aerobic organisms. The same transformation is achieved in anaerobic organisms by EC, anaerobic magnesium-protoporphyrin IX monomethyl ester cyclase. Some facultative phototrophic bacteria, such as Rubrivivax gelatinosus, possess both enzymes.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 92353-62-3


1. Walker, C.J., Mansfield, K.E., Rezzano, I.N., Hanamoto, C.M., Smith, K.M. and Castelfranco, P.A. The magnesium-protoporphyrin IX (oxidative) cyclase system. Studies on the mechanism and specificity of the reaction sequence. Biochem. J. 255 (1988) 685-692. [PMID: 3202840]

2. Bollivar, D.W. and Beale, S.I. The chlorophyll biosynthetic enzyme Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase (characterization and partial purification from Chlamydomonas reinhardtii and Synechocystis sp. PCC 6803). Plant Physiol. 112 (1996) 105-114. [PMID: 12226378]

3. Pinta, V., Picaud, M., Reiss-Husson, F. and Astier, C. Rubrivivax gelatinosus acsF (previously orf358) codes for a conserved, putative binuclear-iron-cluster-containing protein involved in aerobic oxidative cyclization of Mg-protoporphyrin IX monomethylester. J. Bacteriol. 184 (2002) 746-753. [PMID: 11790744]

4. Tottey, S., Block, M.A., Allen, M., Westergren, T., Albrieux, C., Scheller, H.V., Merchant, S. and Jensen, P.E. Arabidopsis CHL27, located in both envelope and thylakoid membranes, is required for the synthesis of protochlorophyllide. Proc. Natl. Acad. Sci. USA 100 (2003) 16119-16124. [PMID: 14673103]

[EC created 2003, modified 2017]

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