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Information on EC 6.6.1.1 - magnesium chelatase and Organism(s) Rhodobacter capsulatus and UniProt Accession P26239
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6.6.1.1 magnesium chelataseIUBMB Comments
This is the first committed step of chlorophyll biosynthesis and is a branchpoint of two major routes in the tetrapyrrole pathway.
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Word Map
- 6.6.1.1
- chlorophyll
- chloroplast
- tetrapyrrole
- rhodobacter
- protochlorophyllide
- gun4
- bacteriochlorophyll
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5-aminolevulinic
- phytoene
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ferrochelatase
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chlorophyll-deficient
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plastid-to-nucleus
- chlorophyllide
- chlm
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pale-green
- geminivirus
- thermosynechococcus
- protoporphyrinogen
- agriculture
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semi-dominant
The taxonomic range for the selected organisms is: Rhodobacter capsulatus
The expected taxonomic range for this enzyme is: Bacteria, Eukaryota, Archaea
The expected taxonomic range for this enzyme is: Bacteria, Eukaryota, Archaea
Reaction Schemes
+
+
+
=
+
+
+
2
Synonyms
magnesium chelatase, mg-chelatase, mg chelatase, chli1, xantha-f, abar/chlh, magnesium-chelatase, mg-chelatase h, chelatase h subunit, h subunit of mg-chelatase, 
more
topSYNONYM 
ORGANISM
UNIPROT
COMMENTARY 
LITERATURE
BchI
38 kDa subunit I, Mg-chelatase consists of three subunits BchH, BchD and BchI, subunits D and I form the AAA+ motor complex in the presence of ATP and Mg2+, whereas subunit H binds protoporphyrin IX
magnesium-chelatase
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magnesium-protoporphyrin chelatase
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magnesium-protoporphyrin IX chelatase
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Mg-chelatase
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Mg-protoporphyrin IX magnesio-lyase
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protoporphyrin IX magnesium-chelatase
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protoporphyrin IX Mg-chelatase
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
ATP + protoporphyrin IX + Mg2+ + H2O = ADP + phosphate + Mg-protoporphyrin IX + 2 H+
subunits H, I and D from bchH, bchI and bchD genes combine to form the enzyme complex, the complex is active only when the three proteins are present
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ATP + protoporphyrin IX + Mg2+ + H2O = ADP + phosphate + Mg-protoporphyrin IX + 2 H+
complex three-subunit enzyme
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ATP + protoporphyrin IX + Mg2+ + H2O = ADP + phosphate + Mg-protoporphyrin IX + 2 H+
complex three-subunit enzyme
ATP + protoporphyrin IX + Mg2+ + H2O = ADP + phosphate + Mg-protoporphyrin IX + 2 H+
this is the first committed step of chlorophyll biosynthesis and is a branchpoint of two major routes in the tetrapyrrole pathway
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
Ligation
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-
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PATHWAY SOURCE
PATHWAYS
BRENDA
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-, -, -
SYSTEMATIC NAME
IUBMB Comments
Mg-protoporphyrin IX magnesium-lyase
This is the first committed step of chlorophyll biosynthesis and is a branchpoint of two major routes in the tetrapyrrole pathway.
CAS REGISTRY NUMBER
COMMENTARY
9074-88-8
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SUBSTRATE
PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
ATP + deuteroporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-deuteroporphyrin IX + H+
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-
-
-
?
ATP + deuteroporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-deuteroporphyrin IX + H+
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ATP utilization by magnesium chelatase is solely connected to the I-subunit
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-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
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-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
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-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
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-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
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-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
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optimum activity at 11.5 mM Mg2+
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?
additional information
?
-
BchH is the rate-limiting component of Mg chelatase in cell extracts, and its slective inactivation during adaption to aerobic growth may account for the rapid inactivation of Mg chelatase in vivo when anaerobically growing cells are exposed to O2 in the light
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-
?
additional information
?
-
-
BchH is the rate-limiting component of Mg chelatase in cell extracts, and its slective inactivation during adaption to aerobic growth may account for the rapid inactivation of Mg chelatase in vivo when anaerobically growing cells are exposed to O2 in the light
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-
?
additional information
?
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enzyme is composed of subunits BchI, BchD, BchH. The BchIBchD complex has intrinsic ATPase activity, and addition of BchH greatly increased ATPase activity. This is concentration-dependent and gives sigmoidal kinetics. ATPase activity is about 40fold higher than magnesium chelatase activity and continues despite cessation of magnesium chelation, implying secondary roles for ATP hydrolysis. Porphyrin binding is the rate limiting step in catalysis
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?
additional information
?
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BchJ may serve as an Mg-protoporphyrin carrier between the BchH Mg-protoporphyrin and BchM
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-
?
additional information
?
-
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BchJ may serve as an Mg-protoporphyrin carrier between the BchH Mg-protoporphyrin and BchM
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-
?
NATURAL SUBSTRATE
NATURAL PRODUCT
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate)
(Substrate)
LITERATURE
(Substrate)
(Substrate)
COMMENTARY
(Product)
(Product)
LITERATURE
(Product)
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
r=reversible
ir=irreversible
?=not specified
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
-
?
ATP + protoporphyrin IX + Mg2+ + H2O
ADP + phosphate + Mg-protoporphyrin IX + H+
-
-
?
additional information
?
-
BchH is the rate-limiting component of Mg chelatase in cell extracts, and its slective inactivation during adaption to aerobic growth may account for the rapid inactivation of Mg chelatase in vivo when anaerobically growing cells are exposed to O2 in the light
-
-
?
additional information
?
-
-
BchH is the rate-limiting component of Mg chelatase in cell extracts, and its slective inactivation during adaption to aerobic growth may account for the rapid inactivation of Mg chelatase in vivo when anaerobically growing cells are exposed to O2 in the light
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-
?
METALS and IONS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
INHIBITOR
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
Urea
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20% inhibition with 100 mM, 50% inhibition with 250 mM, 90% inhibition with 800 mM
ACTIVATING COMPOUND
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
IMAGE
pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
TEMPERATURE OPTIMUM
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
ORGANISM
COMMENTARY
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
GENERAL INFORMATION
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
metabolism
Mg-chelatase catalyzes the first step of the chlorophyll biosynthetic pathway
PDB
SCOP
CATH
UNIPROT
ORGANISM
MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
140000
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1 * 40000 (I-subunit) + 1 * 70000 (D-subunit) + 1 * 140000 (H-subunit)
40000
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1 * 40000 (I-subunit) + 1 * 70000 (D-subunit) + 1 * 140000 (H-subunit)
70000
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1 * 40000 (I-subunit) + 1 * 70000 (D-subunit) + 1 * 140000 (H-subunit)
SUBUNIT
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
trimer
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1 * 40000 (I-subunit) + 1 * 70000 (D-subunit) + 1 * 140000 (H-subunit)
additional information
additional information
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the enzyme has three subunits, BchI, BchH and BchD
additional information
-
the enzyme has three subunits, BchI, BchH and BchD
additional information
-
enzyme is composed of subunits BchI, BchD, BchH. The BchIBchD complex has intrinsic ATPase activity, and addition of BchH greatly increased ATPase activity. This is concentration-dependent and gives sigmoidal kinetics. ATPase activity is about 40fold higher than magnesium chelatase activity and continues despite cessation of magnesium chelation, implying secondary roles for ATP hydrolysis
CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
subunit BchH, at 25 A resolution. The apo structure contains three major lobe-shaped domains connected at a single point with additional densities at the tip of two lobes termed the thumb and finger. The substrate-bound BchH complex BchH Proto shows a distinct conformational change in the thumb and finger subdomains. Prolonged proteolysis of native apo-BchH produces a stable C-terminal fragment of 45 kDa, and protoporphyrin protects the full-length polypeptide from degradation
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PROTEIN VARIANTS
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
D207N
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BchI mutant forms a complex with wild-type BchD. Mutant shows 7.2% of wild-type ATPase activity. Mutant is deficient of magnesium chelatase activity
L111F
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BchI mutant forms a complex with wild-type BchD. Mutant shows 5.5% of wild-type ATPase activity. Mutant is deficient of magnesium chelatase activity
R289K
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BchI mutant forms a complex with wild-type BchD. Mutant shows 10.9% of wild-type ATPase activity. Mutant is deficient of magnesium chelatase activity
V113G
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BchI mutant forms a complex with wild-type BchD. Mutant shows 25% of wild-type ATPase activity. Mutant shows magnesium chelatase activity. Magnesium chelatase assays containing a mixture of mutant BchI V113G and wild-type BchI have the effect of stimulating the activity
additional information
-
mixing experiments with modified and wild-type BchI in various combinations show that an exchange of BchI subunits in magnesium chelatase occurs during the catalytic cycle, indicating that a dissociation of the complex may be part of the reaction mechanism
pH STABILITY
ORGANISM
UNIPROT
COMMENTARY
LITERATURE
PURIFICATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
HisTrap Ni2+ crude FF chelating column chromatography, gel filtration
CLONED (Commentary)
ORGANISM
UNIPROT
LITERATURE
BchD, BchI and BchH proteins are expressed in Escherichia coli from the respective cloned Rhodobacter capsulatus genes
expression of bchD gene in Escherichia coli
REF.
AUTHORS
TITLE
JOURNAL
VOL.
PAGES
YEAR
ORGANISM (UNIPROT)
PUBMED ID
SOURCE
Walker, C.J.; Willows, R.D.
Mechanism and regulation of Mg-chelatase
Biochem. J.
327
321-333
1997
Arabidopsis thaliana, Cucumis sativus, Hordeum vulgare, Pisum sativum, Rhodobacter capsulatus, Cereibacter sphaeroides, Synechocystis sp. (P51634)
Fodje, M.N.; Hansson, A.; Hansson, M.; Olsen, J.G.; Gough, S.; Willows, R.D.; Al-Karadaghi, S.
Interplay between an AAA module and an integrin I domain may regulate the function of magnesium chelatase
J. Mol. Biol.
311
111-122
2001
Rhodobacter capsulatus
Gorchein, A.
Cell-free activity of magnesium chelatase in Rhodobacter spheroides and Rhodobacter capsulatus
Biochem. Soc. Trans.
25
82S
1997
Rhodobacter capsulatus, Cereibacter sphaeroides
Willows, R.D.; Lake, V.; Roberts, T.H.; Beale, S.I.
Inactivation of Mg chelatase during transition from anaerobic to aerobic growth in Rhodobacter capsulatus
J. Bacteriol.
185
3249-3258
2003
Rhodobacter capsulatus (P26162), Rhodobacter capsulatus, Rhodobacter capsulatus SB1003 (P26162)
Willows, R.D.; Beale, S.I.
Heterologous expression of the Rhodobacter capsulatus BchI, -D, and -H genes that encode magnesium chelatase subunits and characterization of the reconstituted enzyme
J. Biol. Chem.
273
34206-34213
1998
Rhodobacter capsulatus
Papenbrock, J.; Mock, H.P.; Tanaka, R.; Kruse, E.; Grimm, B.
Role of magnesium chelatase activity in the early steps of the tetrapyrrole biosynthetic pathway
Plant Physiol.
122
1161-1169
2000
Nicotiana tabacum, Rhodobacter capsulatus
Willows, R.D.; Hansson, A.; Birch, D.; Al-Karadaghi, S.; Hansson, M.
EM single particle analysis of the ATP-dependent BchI complex of magnesium chelatase: an AAA+ hexamer
J. Struct. Biol.
146
227-233
2004
Rhodobacter capsulatus
Sirijovski, N.; Olsson, U.; Lundqvist, J.; Al-Karadaghi, S.; Willows, R.D.; Hansson, M.
ATPase activity associated with the magnesium chelatase H-subunit of the chlorophyll biosynthetic pathway is an artefact
Biochem. J.
400
477-484
2006
Rhodobacter capsulatus
Sirijovski, N.; Lundqvist, J.; Rosenbaeck, M.; Elmlund, H.; Al-Karadaghi, S.; Willows, R.D.; Hansson, M.
Substrate-binding model of the chlorophyll biosynthetic magnesium chelatase BchH subunit
J. Biol. Chem.
283
11652-11660
2008
Rhodobacter capsulatus
Sawicki, A.; Willows, R.D.
Kinetic analyses of the magnesium chelatase provide insights into the mechanism, structure, and formation of the complex
J. Biol. Chem.
283
31294-31302
2008
Rhodobacter capsulatus
Lundqvist, J.; Elmlund, H.; Wulff, R.P.; Berglund, L.; Elmlund, D.; Emanuelsson, C.; Hebert, H.; Willows, R.D.; Hansson, M.; Lindahl, M.; Al-Karadaghi, S.
ATP-induced conformational dynamics in the AAA+ motor unit of magnesium chelatase
Structure
18
354-365
2010
Rhodobacter capsulatus (P26239), Rhodobacter capsulatus
Sawicki, A.; Willows, R.D.
BchJ and BchM interact in a 1: 1 ratio with the magnesium chelatase BchH subunit of Rhodobacter capsulatus
FEBS J.
277
4709-4721
2010
Rhodobacter capsulatus (P26162), Rhodobacter capsulatus
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