Rieske non-heme iron oxygenase (RO) family, Pheophorbide a oxygenase (PaO) subfamily, N-terminal Rieske domain of the oxygenase alpha subunit; composed of the oxygenase alpha subunits of a small subfamily of enzymes found in plants as well as oxygenic cyanobacterial photosynthesizers including LLS1 (lethal leaf spot 1, also known as PaO) and ACD1 (accelerated cell death 1). ROs comprise a large class of aromatic ring-hydroxylating dioxygenases that enable microorganisms to tolerate and utilize aromatic compounds for growth. The oxygenase alpha subunit contains an N-terminal Rieske domain with an [2Fe-2S] cluster and a C-terminal catalytic domain with a mononuclear Fe(II) binding site. The Rieske [2Fe-2S] cluster accepts electrons from a reductase or ferredoxin component and transfers them to the mononuclear iron for catalysis. PaO expression increases upon physical wounding of plant leaves and is thought to catalyze a key step in chlorophyll degradation. The Arabidopsis-accelerated cell death gene ACD1 is involved in oxygenation of PaO.
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