Reaction: pheophorbide a + 2 reduced ferredoxin [iron-sulfur] cluster + 2 H+ + O2 = red chlorophyll catabolite + 2 oxidized ferredoxin [iron-sulfur] cluster (overall reaction)
(1a) pheophorbide a + 2 reduced ferredoxin [iron-sulfur] cluster + 2 H+ + O2 = epoxypheophorbide a + 2 oxidized ferredoxin [iron-sulfur] cluster + H2O
(1b) epoxypheophorbide a + H2O = red chlorophyll catabolite (spontaneous)
For diagram of reaction click here.
Glossary: red chlorophyll catabolite = RCC = (7S,8S,101R)-8-(2-carboxyethyl)-8,23-dihydro-17-ethyl-19-formyl-101-(methoxycarbonyl)-3,7,13,18-tetramethyl-2-vinyl-7H-10,12-ethanobiladiene-ab-1,102(21H)-dione
Other name(s): pheide a monooxygenase; pheide a oxygenase; PaO; PAO
Systematic name: pheophorbide-a,ferredoxin:oxygen oxidoreductase (biladiene-forming)
Comments: This enzyme catalyses a key reaction in chlorophyll degradation, which occurs during leaf senescence and fruit ripening in higher plants. The enzyme from Arabidopsis contains a Rieske-type iron-sulfur cluster [2] and requires reduced ferredoxin, which is generated either by NADPH through the pentose-phosphate pathway or by the action of photosystem I [4]. While still attached to this enzyme, the product is rapidly converted into primary fluorescent chlorophyll catabolite by the action of EC 1.3.7.12, red chlorophyll catabolite reductase [2,6]. Pheophorbide b acts as an inhibitor. In 18O2 labelling experiments, only the aldehyde oxygen is labelled, suggesting that the other oxygen atom may originate from H2O [1].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Hörtensteiner, S., Wüthrich, K.L., Matile, P., Ongania, K.H. and Kräutler, B. The key step in chlorophyll breakdown in higher plants. Cleavage of pheophorbide a macrocycle by a monooxygenase. J. Biol. Chem. 273 (1998) 15335-15339. [PMID: 9624113]
2. Pružinská, A., Tanner, G., Anders, I., Roca, M. and Hörtensteiner, S. Chlorophyll breakdown: pheophorbide a oxygenase is a Rieske-type iron-sulfur protein, encoded by the accelerated cell death 1 gene. Proc. Natl. Acad. Sci. USA 100 (2003) 15259-15264. [PMID: 14657372]
3. Chung, D.W., Pružinská, A., Hörtensteiner, S. and Ort, D.R. The role of pheophorbide a oxygenase expression and activity in the canola green seed problem. Plant Physiol. 142 (2006) 88-97. [PMID: 16844830]
4. Rodoni, S., Mühlecker, W., Anderl, M., Kräutler, B., Moser, D., Thomas, H., Matile, P. and Hörtensteiner, S. Chlorophyll breakdown in senescent chloroplasts. Cleavage of pheophorbide a in two enzymic steps. Plant Physiol. 115 (1997) 669-676. [PMID: 12223835]
5. Hörtensteiner, S. Chlorophyll degradation during senescence. Annu. Rev. Plant Biol. 57 (2006) 55-77. [PMID: 16669755]
6. Pružinská, A., Anders, I., Aubry, S., Schenk, N., Tapernoux-Lüthi, E., Müller, T., Kräutler, B. and Hörtensteiner, S. In vivo participation of red chlorophyll catabolite reductase in chlorophyll breakdown. Plant Cell 19 (2007) 369-387. [PMID: 17237353]