Linked Life Data

1991124

Source:http://linkedlifedata.com/resource/pubmed/id/1991124

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
1991-3-14
pubmed:abstractText
The active sites of all bacterial and vertebrate dihydrofolate reductases that have been examined have a tryptophan residue near the binding sites for NADPH and dihydrofolate. In cases where the three-dimensional structure has been determined by X-ray crystallography, this conserved tryptophan residue makes hydrophobic and van der Waals interactions with the nicotinamide moiety of bound NADPH, and its indole nitrogen interacts with the C4 oxygen of bound folate through a bridge provided by a bound water molecule. We have addressed the question of why even the very conservative replacement of this tryptophan by phenylalanine does not seem to occur naturally. Human dihydrofolate reductase with this replacement of tryptophan by phenylalanine has increased rate constants for dissociation of substrates and products and a considerably decreased rate of hydride transfer. These cause some changes in steady-state kinetic behavior, including substantial increases in Michaelis constants for NADPH and dihydrofolate, but there is also a 3-fold increase in kcat. The branched mechanistic pathway for this enzyme has been completely defined and is sufficiently different from that of wild-type enzyme to cause changes in some transient-state kinetics. The most critical changes resulting from the amino acid substitution appear to be a 50% decrease in stability and a decrease in efficiency from 69% to 21% under intracellular conditions.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
5
pubmed:volume
30
pubmed:geneSymbol
DHFR
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1432-40
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1991
pubmed:articleTitle
Role of the conserved active site residue tryptophan-24 of human dihydrofolate reductase as revealed by mutagenesis.
pubmed:affiliation
Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't