title: Pattern of expression and substrate specificity of chloroplast ferredoxins from Chlamydomonas reinhardtii.
abstract: Ferredoxin (Fd) is the major iron-containing protein in photosynthetic organisms and is central to reductive metabolism in the chloroplast. The Chlamydomonas reinhardtii genome encodes six plant type [Fe2S2] ferredoxins, products of PETF, FDX2-FDX6. We performed the functional analysis of these ferredoxins by localizing Fd, Fdx2, Fdx3, and Fdx6 to the chloroplast by using isoform-specific antibodies and monitoring the pattern of gene expression by iron and copper nutrition, nitrogen source, and hydrogen peroxide stress. In addition, we also measured the midpoint redox potentials of Fd and Fdx2 and determined the kinetic parameters of their reactions with several ferredoxin-interacting proteins, namely nitrite reductase, Fd:NADP+ oxidoreductase, and Fd:thioredoxin reductase. We found that each of the FDX genes is differently regulated in response to changes in nutrient supply. Moreover, we show that Fdx2 (Em = -321 mV), whose expression is regulated by nitrate, is a more efficient electron donor to nitrite reductase relative to Fd. Overall, the results suggest that each ferredoxin isoform has substrate specificity and that the presence of multiple ferredoxin isoforms allows for the allocation of reducing power to specific metabolic pathways in the chloroplast under various growth conditions.
authors: Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1569, USA.
authors: Aimee M
authors: AM
authors: Terauchi
authors: Shu-Fen
authors: SF
authors: Lu
authors: Mirko
authors: M
authors: Zaffagnini
authors: Shane
authors: S
authors: Tappa
authors: Masakazu
authors: M
authors: Hirasawa
authors: Jatindra N
authors: JN
authors: Tripathy
authors: David B
authors: DB
authors: Knaff
authors: Patrick J
authors: PJ
authors: Farmer
authors: Stéphane D
authors: SD
authors: Lemaire
authors: Toshiharu
authors: T
authors: Hase
authors: Sabeeha S
authors: SS
authors: Merchant
mesh_terms: D020418:Algal Proteins / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism*; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D005288:Ferredoxins / Q000096:biosynthesis* / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D054628:Genome, Chloroplast / Q000502:physiology; D006861:Hydrogen Peroxide / Q000493:pharmacokinetics; D007501:Iron / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D020418:Algal Proteins; D005288:Ferredoxins; D016877:Oxidants; D015800:Protozoan Proteins; D003300:Copper; D006861:Hydrogen Peroxide; D007501:Iron; D010088:Oxidoreductases