Linked Life Data

15051720

Source:http://linkedlifedata.com/resource/pubmed/id/15051720

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
26
pubmed:dateCreated
2004-6-21
pubmed:abstractText
The first committed step in chlorophyll biosynthesis is catalyzed by magnesium chelatase, a complex enzyme with at least three substrates, cooperative Mg(2+) activation, and free energy coupling between ATP hydrolysis and metal-ion chelation. A detailed functional study of the behavior of the intact magnesium chelatase has been performed, including characterization of magnesium cooperativity and the stoichiometry of ATP consumption in relation to the magnesium porphyrin produced. It is demonstrated that, in vitro, this catalyzed reaction requires hydrolysis of approximately 15 MgATP(2-) and that the chelation partial reaction is energetically unfavorable, under our assay conditions, with a DeltaG degrees ' of 25-33 kJ mol(-1). Given the likely metabolite concentrations in vivo, this results in the chelatase reaction operating far from equilibrium. We have also determined the steady-state kinetic behavior of the intact enzyme and have compared the kinetic parameters obtained with those observed for the partial reactions of individual subunits. K(DIX) (where D(IX) represents deuteroporphyrin IX) is estimated to be 3.20 microm, and K(MgATP)(2-) is 0.45 mm. k(cat) for chelation is estimated to be 0.8 min(-1), suggesting that the ATP hydrolysis catalyzed by the isolated ChlI subunit is substantially slower in the intact chelatase. The magnesium-rich form of the chelatase is a more effective catalyst of the chelation reaction; magnesium activation of the chelatase increases V, as well as the specificity constant for the reaction of MgATP(2-) and D(IX), possibly as a result of a magnesium-triggered conformational change.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
25
pubmed:volume
279
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
26893-9
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
2004
pubmed:articleTitle
Magnesium-dependent ATPase activity and cooperativity of magnesium chelatase from Synechocystis sp. PCC6803.
pubmed:affiliation
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't