ATPase activity associated with the magnesium chelatase H-subunit of the chlorophyll biosynthetic pathway is an artefact.

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Sirijovski N, Olsson U, Lundqvist J, Al-Karadaghi S, Willows RD, Hansson M

ATPase activity associated with the magnesium chelatase H-subunit of the chlorophyll biosynthetic pathway is an artefact.

Biochem J. 2006 Dec 15;400(3):477-84.

PubMed ID
16928192 [ View in PubMed
]
Abstract

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.

DrugBank Data that Cites this Article

Drug Targets
DrugTargetKindOrganismPharmacological ActionActions
Magnesium acetateSodium/potassium-transporting ATPase subunit alpha-1ProteinHumans
Unknown
Not AvailableDetails
Magnesium cationSodium/potassium-transporting ATPase subunit alpha-1ProteinHumans
Unknown
Not AvailableDetails
Magnesium lactateSodium/potassium-transporting ATPase subunit alpha-1ProteinHumans
Unknown
Not AvailableDetails
Magnesium levulinateSodium/potassium-transporting ATPase subunit alpha-1ProteinHumans
Unknown
Not AvailableDetails