IUBMB Enzyme Nomenclature


Accepted name: chlorophyllide-a oxygenase

Reaction: chlorophyllide a + 2 O2 + 2 NADPH + 2 H+ = chlorophyllide b + 3 H2O + 2 NADP+ (overall reaction)
(1a) chlorophyllide a + O2 + NADPH + H+ = 71-hydroxychlorophyllide a + H2O + NADP+
(1b) 71-hydroxychlorophyllide a + O2 + NADPH + H+ = chlorophyllide b + 2 H2O + NADP+

For diagram of reaction click here.

Other name(s): chlorophyllide a oxygenase; chlorophyll-b synthase; CAO

Systematic name: chlorophyllide-a:oxygen 71-oxidoreductase

Comments: Chlorophyll b is required for the assembly of stable light-harvesting complexes (LHCs) in the chloroplast of green algae, cyanobacteria and plants [2,3]. Contains a mononuclear iron centre [3]. The enzyme catalyses two successive hydroxylations at the 7-methyl group of chlorophyllide a. The second step yields the aldehyde hydrate, which loses H2O spontaneously to form chlorophyllide b [2]. Chlorophyll a and protochlorophyllide a are not substrates [2].

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number: 216503-73-0


1. Espineda, C.E., Linford, A.S., Devine, D. and Brusslan, J.A. The AtCAO gene, encoding chlorophyll a oxygenase, is required for chlorophyll b synthesis in Arabidopsis thaliana. Proc. Natl. Acad. Sci. USA 96 (1999) 10507-10511. [PMID: 10468639]

2. Oster, U., Tanaka, R., Tanaka, A. and Rüdiger, W. Cloning and functional expression of the gene encoding the key enzyme for chlorophyll b biosynthesis (CAO) from Arabidopsis thaliana. Plant J. 21 (2000) 305-310. [PMID: 10758481]

3. Eggink, L.L., LoBrutto, R., Brune, D.C., Brusslan, J., Yamasato, A., Tanaka, A. and Hoober, J.K. Synthesis of chlorophyll b: localization of chlorophyllide a oxygenase and discovery of a stable radical in the catalytic subunit. BMC Plant Biol. 4 (2004) 5. [PMID: 15086960]

4. Porra, R.J., Schafer, W., Cmiel, E., Katheder, I. and Scheer, H. The derivation of the formyl-group oxygen of chlorophyll b in higher plants from molecular oxygen. Achievement of high enrichment of the 7-formyl-group oxygen from 18O2 in greening maize leaves. Eur. J. Biochem. 219 (1994) 671-679. [PMID: 8307032]

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