Open AccessKinetics of the oxidation of ferrocyanide by lactoperoxidase compound II
Author(s) -
KARDEL Danilo M.,
DUNFORD H. Brian,
ALEXANDRE Stéphane
Publication year - 1990
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1990.tb19451.x
Subject(s) - ferrocyanide , chemistry , potassium ferrocyanide , reaction rate constant , kinetics , inorganic chemistry , ionic strength , analytical chemistry (journal) , lactoperoxidase , order of reaction , chromatography , organic chemistry , peroxidase , electrode , aqueous solution , physics , quantum mechanics , enzyme
The kinetics of the oxidation of ferrocyanide by lactoperoxidase compound II has been studied over the pH range 5.2 – 9.9 at 25°C and an ionic strength of 0.11 M. For all pH values, exponential decay curves are obtained for the reaction of compound II in the presence of ferrocyanide which yielded pseudo‐first‐order rate constants K obs . The spontaneous decay of compound II in the absence of ferrocyanide occurs at an appreciable rate which was measured independently and used in the data analysis. At all pH values two striking effects were observed when the rate of the decay reaction in the presence of ferrocyanide, K obs , was plotted against ferrocyanide concentration: a saturation effect and positive intercepts which are attributable to the spontaneous decay. The plots of K obs versus ferrocyanide concentration were analyzed in terms of the following parameters: a first‐order rate constant K 3,obs , a Michaelis constant K m,obs and a spontaneous‐decay rate constant k 4 . The parameters k 3,obs and K m,obs describe the reaction of compound II with ferrocyanide, independently of the spontaneous decay. The parameter k 4 has only a small pH dependence, whereas plots of the logs of k 3,obs and K m,obs versus pH have slopes of – 1 at high pH. The major part of the pH dependence can be explained by the influence of a single heme‐linked acid group in the LPO‐compound‐II – ferrocyanide complex.