Linked Life Data

15147181

Source:http://linkedlifedata.com/resource/pubmed/id/15147181

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
20
pubmed:dateCreated
2004-5-18
pubmed:abstractText
The Saccharomyces cerevisiae Tmt1 gene product is the yeast homologue of the Escherichia coli enzyme that catalyzes the methyl esterification of trans-aconitate, a thermodynamically favored isomer of cis-aconitate and an inhibitor of the citric acid cycle. It has been proposed that methylation may attenuate trans-aconitate inhibition of aconitase and other enzymes of the cycle. Although trans-aconitate is a minor endogenous substrate of the Tmt1 enzyme in extracts of S. cerevisiae, the major endogenous substrate has yet to be identified. We show here that a trimethylsilylated derivative of the major methylated endogenous product of Tmt1 in yeast extracts has an identical gas chromatography retention time and an identical electron impact mass spectrum as one of the two possible monomethyl ester derivatives of (2R,3S)-3-isopropylmalate. (2R,3S)-3-Isopropylmalate is an intermediate of the leucine biosynthetic pathway that shares similar intermediates and reaction chemistry with the portion of the citric acid cycle from oxaloacetate to alpha-ketoglutarate via cis-aconitate. The Tmt1 methyltransferase recognizes (2R,3S)-3-isopropylmalate with similar kinetics as it does trans-aconitate, with respective K(m) values of 127 and 53 microM and V(max) values of 59 and 70 nmol min(-1) mg(-1) of protein in a Tmt1-overexpressed yeast extract. However, we found that isopropylfumarate, the direct homologue of trans-aconitate in the leucine biosynthetic pathway, was at best a very poor substrate for the Tmt1 yeast enzyme. Similarly, the direct homologue of 3-isopropylmalate in the citric acid cycle, isocitrate, is also a very poor substrate. This apparent change in specificity between the intermediates of these two pathways can be understood in terms of the binding of these substrates to the active site. These results suggest that the Tmt1 methyltransferase may work in two different pathways in two different ways: for detoxification in the citric acid cycle and for a possibly novel biosynthetic branch reaction of the leucine biosynthetic pathway.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
25
pubmed:volume
43
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
5976-86
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2004
pubmed:articleTitle
3-Isopropylmalate is the major endogenous substrate of the Saccharomyces cerevisiae trans-aconitate methyltransferase.
pubmed:affiliation
Department of Chemistry and Biochemistry, the Molecular Biology Institute, Los Angeles, California 90095-1570, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't