HOs (haem oxygenases) catalyse the oxidative cleavage of haem to BV (biliverdin), iron and carbon monoxide. In plants, the product of the reaction is BV IXα, the precursor of the PHY (phytochrome) chromophore and is thus essential for proper photomorphogenesis. Arabidopsis thaliana contains one major biochemically characterized HO (HY1) and three additional putative HOs (HO2, HO3 and HO4). All four proteins are encoded in the nucleus but contain chloroplast translocation sequences at their N-termini. The transit peptides of all four proteins are sufficient for chloroplast translocalization as shown by GFP (green fluorescent protein) reporter gene fusions. Overall, all four proteins can be divided into two subfamilies: HO1 and HO2. Here we show that all members of the HO1 subfamily (HY1, HO3 and HO4) are active monomeric HOs and can convert haem to BV IXα using spinach Fd (ferredoxin) as an electron donor. Addition of a second electron donor, such as ascorbate, led to a 10-fold increase in the haem conversion rate. Furthermore, haem turnover is also promoted by light when spinach thylakoids are present. All HO1 family members displayed similar kinetic parameters indicating they all have a possible involvement in PHY chromophore biosynthesis. HO2 did not yield sufficient amounts of soluble protein and therefore required the construction of a synthetic gene adapted to the codon usage of Escherichia coli. HO2 is unable to bind or degrade haem and therefore it is not a haem oxygenase. However, HO2 shows strong binding of proto IX (protoporphyrin IX), a precursor for both haem and chlorophyll biosynthesis. A possible function of HO2 in the regulation of tetrapyrrole metabolism is discussed.
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Research Article|
December 23 2009
Characterization of the haem oxygenase protein family in Arabidopsis thaliana reveals a diversity of functions
Bjoern Gisk;
Bjoern Gisk
*Physiology of Microorganisms, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany
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Yukiko Yasui;
Yukiko Yasui
†Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
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Takayuki Kohchi;
Takayuki Kohchi
†Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
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Nicole Frankenberg-Dinkel
Nicole Frankenberg-Dinkel
1
*Physiology of Microorganisms, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany
1To whom correspondence should be addressed (email nicole.frankenberg@rub.de).
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Publisher: Portland Press Ltd
Received:
May 21 2009
Revision Received:
October 26 2009
Accepted:
October 27 2009
Accepted Manuscript online:
October 27 2009
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2010 Biochemical Society
2010
Biochem J (2010) 425 (2): 425–434.
Article history
Received:
May 21 2009
Revision Received:
October 26 2009
Accepted:
October 27 2009
Accepted Manuscript online:
October 27 2009
Citation
Bjoern Gisk, Yukiko Yasui, Takayuki Kohchi, Nicole Frankenberg-Dinkel; Characterization of the haem oxygenase protein family in Arabidopsis thaliana reveals a diversity of functions. Biochem J 15 January 2010; 425 (2): 425–434. doi: https://doi.org/10.1042/BJ20090775
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