Linked Life Data

18473451

Source:http://linkedlifedata.com/resource/pubmed/id/18473451

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
22
pubmed:dateCreated
2008-5-29
pubmed:abstractText
The mechanism for the catalytic dismutation of superoxide by the Mn(II) pentaazamacrocyclic compound M40403 ([manganese(II) dichloro-(4 R,9 R,14 R,19 R)-3,10,13,20,26 pentaazatetracyclo [20.3.1.0 (4,9).0 (14,9)] hexacosa-1(26),-22(23),24-triene], SODm1) and two 2,21-dimethyl analogues has been investigated using pulse radiolysis. The initial rate of reaction between superoxide and the manganese compounds was found to be dependent on structure and pH, with the resulting transient adducts possessing spectral characteristics of the metal center being oxidized to Mn(III). Values for the p K a of the transient adducts (p K a = 5.65 +/- 0.05; 5.3 +/- 0.1 and <5 for SODm1, SODm2 and SODm3, respectively) were obtained from spectrophotometric and conductivity measurements. Reaction of these transient adducts with further superoxide was highly structure dependent with the 2 S,21 S-dimethyl derivative (SODm2) being highly catalytically active at pH 7.4 ( k cat = 2.35 x 10 (8) M (-1) s (-1)) compared to SODm1 ( k cat = 3.55 x 10 (6) M (-1) s (-1)). In contrast the 2 R,21 R-dimethyl derivative (SODm3) showed no dismutation catalysis at all. The reaction rates of the initial complexes with HO 2 (*) were significantly lower than with O 2 (*-), and it is proposed that O 2 (*-) is the main reactant in the catalytic cycle at pH 7.4. Variable temperature studies revealed major differences in the thermodynamics of the catalytic cycles involving SODm2 or SODm1. In the case of SODm2, the observed high entropic contribution to the activation energy is indicative of ligand conformational changes during the catalytic step. These results have provided the basis for a new mechanism for the catalytic dismutation of superoxide by Mn(II)-pentaazamacrocycle SOD mimetics.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
1520-5215
pubmed:author
pubmed:issnType
Electronic
pubmed:day
5
pubmed:volume
112
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
4929-35
pubmed:meshHeading
pubmed:year
2008
pubmed:articleTitle
Pulse radiolysis investigation on the mechanism of the catalytic action of Mn(II)-pentaazamacrocycle compounds as superoxide dismutase mimetics.
pubmed:affiliation
Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. a.maroz@auckland.ac.nz
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't