Linked Life Data

19039361

Source:http://linkedlifedata.com/resource/pubmed/id/19039361

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
24
pubmed:dateCreated
2008-11-28
pubmed:abstractText
Orotidine-5'-monophosphate decarboxylase (OMP decarboxylase, ODCase) catalyzes the decarboxylation of orotidine-5'-monophosphate (OMP) to uridine-5'-monophosphate (UMP). Despite extensive enzymological, structural, and computational studies, the mechanism of ODCase remains incompletely characterized. Herein, carbon kinetic isotope effects were measured for both the natural abundance substrate and a substrate mixture synthesized for the purpose of carrying out the remote double label isotope effect procedure, with O2 of the substrate as the remote position. The carbon kinetic isotope effect on enzymatic decarboxylation of this substrate mix was measured to be 1.0199 +/- 0.0007, compared to the value of 1.0289 +/- 0.0009 for natural abundance OMP, revealing an (18)O2 isotope effect of 0.991 +/- 0.001. This value equates to an intrinsic isotope effect of approximately 0.983, using a calculated commitment factor derived from previous isotope effect data. The measured (18)O2 isotope effect requires a mechanism with one or more enzymatic processes, including binding and/or chemistry, that contribute to this substantial inverse isotope effect. (18)O2 kinetic isotope effects were calculated for four proposed mechanisms: decarboxylation preceded by proton transfer to 1) O2; 2) O4; and 3) C5; and 4) decarboxylation without a preceding protonation step. A mechanism involving no pre-decarboxylation step does not appear to have any steps with the necessary substantial inverse (18)O2 effect, thus calling into question any mechanism involving simple direct decarboxylation. Protonation at O2, O4, or C5 are all calculated to proceed with inverse (18)O2 effects, and could contribute to the experimentally measured value. Recent crystal structures indicate that O2 of the substrate appears to be involved in an intricate bonding arrangement involving the substrate phosphoryl group, an enzyme Gln side chain, and a bound water molecule; this interaction likely contributes to the observed isotope effect.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Dec
pubmed:issn
1477-0539
pubmed:author
pubmed:issnType
Electronic
pubmed:day
21
pubmed:volume
6
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
4533-41
pubmed:dateRevised
2010-4-29
pubmed:meshHeading
pubmed:year
2008
pubmed:articleTitle
A substantial oxygen isotope effect at O2 in the OMP decarboxylase reaction: mechanistic implications.
pubmed:affiliation
Department of Chemistry, Youngstown State University, Youngstown, OH 44555, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't, Research Support, N.I.H., Extramural