Reaction: magnesium-protoporphyrin IX 13-monomethyl ester + 3 S-adenosyl-L-methionine + H2O = 3,8-divinyl protochlorophyllide a + 3 5'-deoxyadenosine + 3 L-methionine (overall reaction)
(1a) magnesium-protoporphyrin IX 13-monomethyl ester + S-adenosyl-L-methionine + H2O = 131-hydroxy-magnesium-protoporphyrin IX 13-monomethyl ester + 5'-deoxyadenosine + L-methionine
(1b) 131-hydroxy-magnesium-protoporphyrin IX 13-monomethyl ester + S-adenosyl-L-methionine = 131-oxo-magnesium-protoporphyrin IX 13-monomethyl ester + 5'-deoxyadenosine + L-methionine
(1c) 131-oxo-magnesium-protoporphyrin IX 13-monomethyl ester + S-adenosyl-L-methionine = 3,8-divinyl protochlorophyllide a + 5'-deoxyadenosine + L-methionine
For diagram of reaction click here.
Other name(s): bchE (gene name); MPE cyclase (ambiguous)
Systematic name: magnesium-protoporphyrin-IX 13-monomethyl ester,S-adenosyl-L-methionine:H2O oxidoreductase (hydroxylating)
Comments: This radical AdoMet enzyme participates in the biosynthesis of chlorophyllide a in anaerobic bacteria, catalysing the formation of an isocyclic ring. Contains a [4Fe-4S] cluster and a cobalamin cofactor. The same transformation is achieved in aerobic organisms by the oxygen-dependent EC 1.14.13.81, magnesium-protoporphyrin IX monomethyl ester (oxidative) cyclase. Some facultative phototrophic bacteria, such as Rubrivivax gelatinosus, possess both enzymes.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
References:
1. Yang, Z.M. and Bauer, C.E. Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway. J. Bacteriol. 172 (1990) 5001-5010. [PMID: 2203738]
2. Gough, S.P., Petersen, B.O. and Duus, J.O. Anaerobic chlorophyll isocyclic ring formation in Rhodobacter capsulatus requires a cobalamin cofactor. Proc. Natl. Acad. Sci. USA 97 (2000) 6908-6913. [PMID: 10841582]
3. Ouchane, S., Steunou, A.S., Picaud, M. and Astier, C. Aerobic and anaerobic Mg-protoporphyrin monomethyl ester cyclases in purple bacteria: a strategy adopted to bypass the repressive oxygen control system. J. Biol. Chem. 279 (2004) 6385-6394. [PMID: 14617630]
4. Booker, S.J. Anaerobic functionalization of unactivated C-H bonds. Curr. Opin. Chem. Biol. 13 (2009) 58-73. [PMID: 19297239]