Linked Life Data

10493789

Source:http://linkedlifedata.com/resource/pubmed/id/10493789

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
38
pubmed:dateCreated
1999-10-28
pubmed:abstractText
Previous measurements of the kinetics of oxidation of linoleic acid by soybean lipoxygenase 1 have indicated very large deuterium isotope effects, but have not been able to distinguish the primary isotope effect from the alpha-secondary effect. To address this question, singly deuterated linoleic acid was prepared, and enantiomerically resolved using the enzyme itself. Noncompetitive measurements of the primary deuterium isotope effect give a value of ca. 40 which is temperature-independent. The enthalpy of activation is low and isotope-independent, and there is a large isotope effect on the Arrhenius prefactor. A very large apparent secondary isotope effect (ca. 2.1) is measured with deuterium in the primary position, but a greatly reduced value (1.1) is observed with protium in the primary position. Mutagenesis of the active site leads to a significant reduction in k(cat) and perturbed isotope effects, in particular, a secondary effect of 5.6 when deuterium is in the primary position. The anomalous secondary isotope effects are shown to arise from imperfect stereoselectivity of hydrogen abstraction which, for the mutant, is attributed to a combination of inverse substrate binding and increased flexibility at the reactive carbon. After correction, a very large primary (76-84) and small secondary (1.1-1.2) kinetic isotope effects are calculated for both mutant and wild-type enzymes. The weight of the evidence is taken to favor hydrogen tunneling as the primary mechanism of hydrogen transfer.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Sep
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
21
pubmed:volume
38
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
12218-28
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1999
pubmed:articleTitle
Nature of hydrogen transfer in soybean lipoxygenase 1: separation of primary and secondary isotope effects.
pubmed:affiliation
Department of Chemistry, University of California, Berkeley 94720, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.