Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.14/10213
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- Title
- ATPase activity associated with the magnesium chelatase H-subunit of the chlorophyll biosynthetic pathway is an artefact
- Related
- Biochemical journal, Vol. 400, Issue 3, p.477-484
- DOI
- 10.1042/BJ20061103
- Publisher
- Portland Press
- Date
- 2006
- Author/Creator
- Sirijovski, Nick
- Author/Creator
- Olsson, Ulf
- Author/Creator
- Lundqvist, Joakim
- Author/Creator
- Al-Karadaghi, Salam
- Author/Creator
- Willows, Robert D
- Author/Creator
- Hansson, Mats
- Description
- Magnesium chelatase inserts Mg²⁺ into protoporphyrin IX and is the first unique enzyme of the chlorophyll biosynthetic pathway. It is a heterotrimeric enzyme, composed of I- (40 kDa), D- (70 kDa) and H- (140 kDa) subunits. The I- and D-proteins belong to the family of AAA⁺ (ATPases associated with various cellular activities), but only I-subunit hydrolyses ATP to ADP. The D-subunits provide a platform for the assembly of the I-subunits, which results in a two-tiered hexameric ring complex. However, the D-subunits are unstable in the chloroplast unless ATPase active I-subunits are present. The H-subunit binds protoporphyrin and is suggested to be the catalytic subunit. Previous studies have indicated that the H-subunit also has ATPase activity, which is in accordance with an earlier suggested two-stage mechanism of the reaction. In the present study, we demonstrate that gel filtration chromatography of affinity-purified Rhodobacter capsulatus H-subunit produced in Escherichia coli generates a high- and a low-molecular-mass fraction. Both fractions were dominated by the H-subunit, but the ATPase activity was only found in the high-molecular-mass fraction and magnesium chelatase activity was only associated with the low-molecular-mass fraction. We demonstrated that light converted monomeric low-molecular-mass H-subunit into high-molecular-mass aggregates. We conclude that ATP utilization by magnesium chelatase is solely connected to the I-subunit and suggest that a contaminating E. coli protein, which binds to aggregates of the H-subunit, caused the previously reported ATPase activity of the H-subunit.
- Description
- 8 page(s)
- Subject Keyword
- ATPases associated with various cellular activities (AAA⁺)
- Subject Keyword
- bchH
- Subject Keyword
- chlorophyll
- Subject Keyword
- magnesium chelatase
- Subject Keyword
- protoporphyrin IX
- Subject Keyword
- Rhodobacter capsulatus
- Resource Type
- journal article
- Organisation
- Macquarie University. Dept. of Chemistry and Biomolecular Sciences
- Identifier
- http://hdl.handle.net/1959.14/10213
- Identifier
- ISSN:1470-8728
- Identifier
- mq-rm-2006000539
- Language
- eng
- Reviewed
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