title: Expression and biochemical properties of a ferredoxin-dependent heme oxygenase required for phytochrome chromophore synthesis.
abstract: The HY1 gene of Arabidopsis encodes a plastid heme oxygenase (AtHO1) required for the synthesis of the chromophore of the phytochrome family of plant photoreceptors. To determine the enzymatic properties of plant heme oxygenases, we have expressed the HY1 gene (without the plastid transit peptide) in Escherichia coli to produce an amino terminal fusion protein between AtHO1 and glutathione S-transferase. The fusion protein was soluble and expressed at high levels. Purified recombinant AtHO1, after glutathione S-transferase cleavage, is a hemoprotein that forms a 1:1 complex with heme. In the presence of reduced ferredoxin, AtHO1 catalyzed the formation of biliverdin IXalpha from heme with the concomitant production of carbon monoxide. Heme oxygenase activity could also be reconstituted using photoreduced ferredoxin generated through light irradiation of isolated thylakoid membranes, suggesting that ferredoxin may be the electron donor in vivo. In addition, AtHO1 required an iron chelator and second reductant, such as ascorbate, for full activity. These results show that the basic mechanism of heme cleavage has been conserved between plants and other organisms even though the function, subcellular localization, and cofactor requirements of heme oxygenases differ substantially.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Muramoto
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Tsurui
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Terry
authors.forename: Akiho
authors.initials: A
authors.lastname: Yokota
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kohchi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism; D001664:Biliverdine / Q000494:pharmacology; D002248:Carbon Monoxide / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005288:Ferredoxins / Q000737:chemistry / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006420:Hemeproteins / Q000235:genetics / Q000378:metabolism; D008027:Light; D010834:Phytochrome / Q000096:biosynthesis*; D018087:Plastids / Q000201:enzymology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D005288:Ferredoxins; D006420:Hemeproteins; D010834:Phytochrome; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing); D005982:Glutathione Transferase; D001664:Biliverdine; D001205:Ascorbic Acid