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Title Secondary sup 18 O isotope effects for hexokinase-catalyzed phosphoryl transfer from ATP
Creator/Author Jones, J.P. ; Weiss, P.M. ; Cleland, W.W. (Univ. of Wisconsin, Madison (USA))
Publication Date1991 Apr 16
OSTI IdentifierOSTI ID: 5399168
Other Number(s)ISSN0006-2960; CODEN: BICHA
Resource TypeJournal Article
Resource RelationBiochemistry ; Vol/Issue: 30:15
Subject550201 -- Biochemistry-- Tracer Techniques; HEXOKINASE-- BIOCHEMICAL REACTION KINETICS;OXYGEN 18-- ISOTOPE EFFECTS; ADENOSINE;ATP;CATALYSIS;HEMIACETAL DEHYDROGENASES;NITROGEN 15;THIN-LAYER CHROMATOGRAPHY;ULTRAVIOLET RADIATION;YEASTS
Related SubjectCHROMATOGRAPHY;ELECTROMAGNETIC RADIATION;ENZYMES;EUMYCOTA;EVEN-EVEN NUCLEI;FUNGI;ISOTOPES;KINETICS;LIGHT NUCLEI;MICROORGANISMS;NITROGEN ISOTOPES;NUCLEI;NUCLEOSIDES;NUCLEOTIDES;ODD-EVEN NUCLEI;ORGANIC COMPOUNDS;OXIDOREDUCTASES;OXYGEN ISOTOPES;PHOSPHORUS-GROUP TRANSFERASES;PHOSPHOTRANSFERASES;PLANTS;RADIATIONS;REACTION KINETICS;RIBOSIDES;SEPARATION PROCESSES;STABLE ISOTOPES;TRANSFERASES
Description/Abstract Secondary {sup 18}O isotope effects in the {gamma}-position of ATP have been measured on phosphoryl transfer catalyzed by yeast hexokinase in an effort to deduce the structure of the transition state.^The isotope effects were measured by the remote-label method with the exocyclic amino group of adenine as the remote label.^With glucose as substrate, the secondary {sup 18}O isotope effect per {sup 18}O was 0.9987 at pH 8.2 and 0.9965 at pH 5.3, which is below the pK of 6.15 seen in the V/K profile for MgATP.^With the slow substrate 1,5-anhydro-D-glucitol, the value was 0.9976 at pH 8.2.^While part of the inverse nature of the isotope effect may result from an isotope effect on binding, the more inverse values when catalysis is made more rate limiting by decreasing the pH or switching to a slower substrate suggest a dissociative transition state for phosphoryl transfer, in agreement with predictions from model chemistry.^The {sup 18}O equilibrium isotope effect for deprotonation of HATP{sup 3{minus}} is 1.0156, while Mg{sup 2+} coordination to ATP{sup 4{minus}} does not appear to be accompanied by an {sup 18}O isotope effect larger than 1.001.
Country of PublicationUnited States
LanguageEnglish
FormatPages: 3634-3639
System Entry Date2001 May 13

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