Linked Life Data

12873152

Source:http://linkedlifedata.com/resource/pubmed/id/12873152

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
29
pubmed:dateCreated
2003-7-22
pubmed:abstractText
A cationic peroxidase was isolated and characterized from the latex of the perennial Mediterranean plant Euphorbia characias. The purified enzyme contained one heme prosthetic group identified as ferric iron-protoporphyrin IX. In addition, the purified peroxidase contained 1 mol of endogenous calcium per mol of enzyme; removal of this calcium ion resulted in almost complete loss of the enzyme activity. However, when excess Ca(2+) was added to the native enzyme the catalytic efficiency was enhanced by 3 orders of magnitude. The mechanism of activation was studied using a wide range of spectroscopic and analytic techniques. Analysis of the steady state by stopped-flow measurements suggests that the main effect of calcium ions is to favor the oxidation of the ferric enzyme by hydrogen peroxide to form compound I, whereas the other steps of the catalytic cycle seem to be affected to a lesser extent. UV/vis absorption spectra and CD measurements show that the heme iron is pentacoordinated high-spin in native enzyme and remains so after the binding of Ca(2+). Only minor changes in the secondary or tertiary structure of the protein could be detected by fluorescence or CD measurements in the presence of Ca(2+) ions, except for a significant perturbation of the Fe(3+) inner sphere geometry, as detected by EPR measurements. We propose that Ca(2+) binding to a low affinity site induces a reorientation of the distal histidine changing the almost inactive form of Euphorbia peroxidase to a high activity form. This is the first example of a peroxidase that responds as an on/off switch to variations in the external Ca(2+) level.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
29
pubmed:volume
42
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
8909-18
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
2003
pubmed:articleTitle
Critical role of Ca2+ ions in the reaction mechanism of Euphorbia characias peroxidase.
pubmed:affiliation
Department of Applied Sciences in Biosystems, University of Cagliari, Italy.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't