Linked Life Data

7696265

Source:http://linkedlifedata.com/resource/pubmed/id/7696265

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
12
pubmed:dateCreated
1995-5-2
pubmed:abstractText
The pH dependence of Escherichia coli aspartate aminotransferase (AATase) has been investigated by the use of site-directed mutants and alternative substrates. Inhibition of the enzyme by CHES and variations in ionic strength are proposed to explain some of the qualitative differences in the published pH dependence of pig cytosolic AATase kinetics [Velick, S. F., & Vavra, J. (1962) J. Biol. Chem. 237, 2109-2122; Kiick, D.M., & Cook, P.F. (1983) Biochemistry 22, 375-382]. The pKa values of the basic limbs in the kcat/KM profiles for the amino acids, L-Asp and L-cysteinesulfinate (L-CS), are identical, within error, to those of free substrates, (L-Asp, pKa = 9.6; L-CS, pKa = 9.0). This pKa therefore is assigned to the alpha-amino group of the substrate. Replacement of the active site base, Lys-258, with the weaker base, gamma-thia-Lys, does not alter the intrinsic pKa for the profiles of the Ki values for the maleate-E.PMP complexes or the kcat/K alpha-KGM values. The mutation Y225F results in an alkaline shift of the pKa in the kcat/K alph-KGM profile. This pKa is assigned to the C4' amino group of PMP. E. coli AATase, unlike pig cytosolic AATase, shows a pH dependence on kcat between pH 5 and 10 that arises from a change in the rate-determining step at pH extremes. C alpha proton abstraction is partially rate-determining at neutral pH values, but not at pH extremes.(ABSTRACT TRUNCATED AT 250 WORDS)
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Mar
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
28
pubmed:volume
34
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
3999-4007
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1995
pubmed:articleTitle
Use of site-directed mutagenesis and alternative substrates to assign the prototropic groups important to catalysis by Escherichia coli aspartate aminotransferase.
pubmed:affiliation
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
pubmed:publicationType
Journal Article, Comparative Study, 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