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Catalyses the two-electron reduction of biliverdin IXalpha. Can use [2Fe-2S] ferredoxins from a number of sources as acceptor but not the [4Fe-4S] ferredoxin from Clostridium pasteurianum. The isomerization of (3Z)-phytochromobilin to (3E)-phytochromobilin is thought to occur prior to covalent attachment to apophytochrome in the plant cell cytoplasm. Flavodoxins can be used instead of ferredoxin.
HY2 synthesizes the open chain tetrapyrrole chromophore for light-sensing phytochromes. It catalyzes the double bond reduction of a heme-derived tetrapyrrole intermediate biliverdin IXalpha at the A-ring diene system
conserved surface-charged residues on HY2 and Arabidopsis ferredoxin AtFd2 are important in the protein-protein interaction as well as biliverdin reduction activity of HY2, mutational analysis, overview. The C12 propionate group of biliverdin is important for HY2-catalyzed biliverdin reduction
development of a system to produce phytochromobilin in Escherichia coli by coexpression of heme oxygenase and phytochromobilin:ferredoxin oxidoreductase in a single operon in conjunction with apophytochrome using two compatible plasmids
overexpression in Synechococcus sp. strain PCC 7002, from endogenous plasmid pAQ1 under the control of the Synechocystis sp. strain PCC 6803 cpcBA promoter, leads to overproduction of phytochromobilin, the cells show a phenotype only slightly less pigmented and blue-green than the wild-type, the strain producing phycobiliproteins carrying phytochromobilin grow much more slowly at low light intensity. Transformant colonies in which pcyA is inactivated in the HY2 overexpression background does not develop a chlorotic appearance, and segregation of the mutant and wild-type alleles is rapidly achieved
recombinant functional expression of HT-HY2 in Escherichia coli with production of phytochromobilin, functional co-expression with cyanobacterial heme oxygenase, and the phycocyanin alpha-subunit, CpcA, from Synechocystis sp. PCC 6803 or Synechococcus sp. PCC 7002, and with the phycocyanin alpha-subunit phycocyanobilin lyase, CpcE/CpcF, or the phycoerythrocyanin alpha-subunit phycocyanobilin isomerizing lyase, PecE/PecF, from Noctoc sp. PCC 7120. Production levels of fluorescent pigments and chromophore analysis, overview