Open AccessIonic Strength Dependence of the Oxidation of Iodide and Ferrocyanide by Compound I of Horseradish Peroxidase
Author(s) -
STEINER Håkan,
DUNFORD H. Brian
Publication year - 1978
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1978.tb12049.x
Subject(s) - ionic strength , chemistry , ferrocyanide , horseradish peroxidase , iodide , reaction rate constant , inorganic chemistry , kinetics , ionic bonding , reaction rate , organic chemistry , catalysis , ion , enzyme , electrode , physics , quantum mechanics , aqueous solution
The kinetics of the oxidation of iodide and ferrocyanide by compound I of horseradish peroxidase have been studied at 25°C as a function of ionic strength and pH. The ionic strength dependencies of the second‐order rate constants are tested with an extended form of the Debye‐Hückel equation for the activity coefficients of the reacting species. For the reaction of iodide with compound I it is shown that the pH variation of the rate constant at zero ionic strength is caused mainly by titrating a catalytically important acid group and not mainly by the varying charge of the protein. The ferrocyanide reaction rate with compound I does not correlate with enzyme net charge, at all pH values. The influence of electrostatic interactions on reaction rates is discussed.