Premium
A Kinetic isotope effect in purinic 8‐CH exchange of guanine nucleotides: Measurement by Raman spectroscopy
Author(s) -
Thomas G. J.,
Lane M. J.
Publication year - 1980
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250090213
Subject(s) - kinetic isotope effect , chemistry , raman spectroscopy , arrhenius equation , kinetic energy , deuterium , analytical chemistry (journal) , isotope , reaction rate constant , guanine , spectroscopy , proton , atmospheric temperature range , activation energy , kinetics , nucleotide , chromatography , thermodynamics , biochemistry , physics , quantum mechanics , optics , gene
Rates of deuterium exchange of the 8‐CH groups of 5′‐rGMP and cGMP in D 2 O solutions ( K H ) are compared with rates of protium exchange of the 8‐CD groups of the same compounds in H 2 O solutions ( K D ). The ratio of the two rate constants ( k H / k D ) defines an isotope effect which is a combination of primary kinetic and solvent isotope effects, the former predominating. The net isotope effect was measured by Raman spectrophotometry over the temperature range 30–80°C. The Arrhenius activation energies ( E a ) and pre‐exponential frequency factors ( A ) were also determined. The average values of k H / k D are 1.82 ± 0.15 for 5′‐rGMP and 1.43 ± 0.06 for cGMP. The relatively small kinetic isotope effects are indicative typically of an unsymmetrical transition state. The ratio E a H / E a Dis unity in both compounds, indicating an early or reactant‐like transition state. The present data are consistent with, and extend the range of, the Bell–Goodall curve relating log ( k H / k D ) to ΔpK of the two acid–base systems involved in the proton transfer during the rate‐determining step.