Linked Life Data

3052578

Source:http://linkedlifedata.com/resource/pubmed/id/3052578

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
15
pubmed:dateCreated
1988-12-22
pubmed:abstractText
The variations with pH of the kinetic parameters and primary deuterium isotope effects for the reaction of NADPH with dihydrofolate reductase from Escherichia coli have been determined. The aims of the investigations were to elucidate the chemical mechanism of the reaction and to obtain information about the location of the rate-limiting steps. The V and V/KNADPH profiles indicate that a single ionizing group at the active center of the enzyme must be protonated for catalysis, whereas the Ki profiles show that the binding of NADPH to the free enzyme and of ATP-ribose to the enzyme-dihydrofolate complex is pH independent. From the results of deuterium isotope effects on V/KNADPH, it is concluded that NADPH behaves as a sticky substrate. It is this stickiness that raises artificially the intrinsic pK value of 6.4 for the Asp-27 residue of the enzyme-dihydrofolate complex [Howell, E. E., Villafranca, J. E., Warren, M. S., Oatley, S. J., & Kraut, J. (1986) Science (Washington, D.C.) 231, 1123] to an observed value of 8.9. Thus, the binary enzyme complex is largely protonated at neutral pH. The elevation of the intrinsic pK value of 6.4 for the ternary enzyme-NADPH-dihydrofolate complex to 8.5 is not due to the kinetic effects of substrates. Rather, it is the consequence of the lower, pH-independent rate of product release and the faster pH-dependent catalytic step. At neutral pH, the proportion of enzyme present as a protonated ternary enzyme-substrate complex is sufficient to keep catalysis faster than product release.(ABSTRACT TRUNCATED AT 250 WORDS)
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
26
pubmed:volume
27
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
5499-506
pubmed:dateRevised
2000-12-18
pubmed:meshHeading
pubmed:year
1988
pubmed:articleTitle
Mechanism of the reaction catalyzed by dihydrofolate reductase from Escherichia coli: pH and deuterium isotope effects with NADPH as the variable substrate.
pubmed:affiliation
Department of Biochemistry, John Curtin School of Medical Research, Australian National University, Canberra City.
pubmed:publicationType
Journal Article