title: Biliverdin reduction by cyanobacterial phycocyanobilin:ferredoxin oxidoreductase (PcyA) proceeds via linear tetrapyrrole radical intermediates.
abstract: Cyanobacterial phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes the four electron reduction of biliverdin IXalpha (BV) to phycocyanobilin, a key step in the biosynthesis of the linear tetrapyrrole (bilin) prosthetic groups of cyanobacterial phytochromes and the light-harvesting phycobiliproteins. Using an anaerobic assay protocol, optically detected bilin-protein intermediates, produced during the PcyA catalytic cycle, were shown to correlate well with the appearance and decay of an isotropic g approximately 2 EPR signal measured at low temperature. Absorption spectral simulations of biliverdin XIIIalpha reduction support a mechanism involving direct electron transfers from ferredoxin to protonated bilin:PcyA complexes.
authors.affiliation: Section of Molecular and Cellular Biology, University of California, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Shih-Long
authors.initials: SL
authors.lastname: Tu
authors.forename: Alexander
authors.initials: A
authors.lastname: Gunn
authors.forename: Michael D
authors.initials: MD
authors.lastname: Toney
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
mesh_terms: D001664:Biliverdine / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism; D005288:Ferredoxins / Q000737:chemistry* / Q000378:metabolism; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000096:biosynthesis / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry* / Q000378:metabolism; D010834:Phytochrome / Q000737:chemistry / Q000378:metabolism; D011758:Pyrroles / Q000737:chemistry* / Q000378:metabolism; D045725:Tetrapyrroles / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005288:Ferredoxins; D005609:Free Radicals; D045342:Light-Harvesting Protein Complexes; D052980:Phycobilins; D011758:Pyrroles; D045725:Tetrapyrroles; D010798:Phycocyanin; D010834:Phytochrome; C011069:phycocyanobilin; D010088:Oxidoreductases; C492097:phycocyanobilin-ferredoxin oxidoreductase, Anabaena; D001664:Biliverdine