Mordechai L. Kremer

Is OH the active Fenton intermediate in the oxidation of ethanol

A re-examination of the data of Rush and Koppenol (J. Inorg. Biochem. 29 (1987) 199) on the competitive oxidation of C2H5OH and Fe2+ by Fentons reagent shows that the ratio of the rate constants of the two reactions is 3.2 and not 6.3. The significance of this finding is that it is not possible to identify the active intermediate in the Fenton reaction with the *OH radical.

The promoting effect of cupric ions on the ferric ion catalyzed decomposition of hydrogen peroxide

Abstract The effect of Cu2+ ions on the Fe3+ ion catalyzed decomposition of H2O2 was reinvestigated. Deviations from steady state, first order kinetics were observed at a higher [H2O2] in the presence of Cu2+ ions. The results are discussed in terms of the mechanism suggested by Kremer and Stein for the catalytic decomposition of H2O2. The promoting action of Cu2+ is due to its acceleration of the conversion of the primary to the secondary iron (III)-H2O2 complex.

Independent activity of catalase haematins.

Abstract The peroxidatic mechanism for the catalytic reaction and for peroxidation has been extended from haematin basis to include the catalase molecule as a whole. It has been shown that interaction among single haematin units does not affect the form of the rate equations for the catalatic reaction. An analysis of the kinetics of the competition of the catalatic and peroxidatic reactions shows, however, that catalase haematins are equivalent and non-interacting during catalysis. The implication of this result in relation to the catalysis by catalase subunits is discussed.

The effect of dimerization on the catalytic activity of haemin

Abstract The effect of dimerization of chloroprotoferrihaem on the catalytic decomposition of H 2 O 2 has been studied. It has been shown that the dimer is catalytically inactive. The equilibrium constant of dimerization is 1 · 10 3 -3 · 10 3 M −1 in the pH range 6.5–8.0 at 0° C. Chloroprotoferrihaem dissolved initially in alkali is more extensively dimerized than that dissolved in phosphate. The possible reason for this difference is discussed.

The acid dissociation of haemin

Abstract The acid dissociation constant of haemin has been determined in the temperature range of 0–30 °C. ΔG°, ΔH° and ΔS° of the dissociation are 11.4 kcal/mole, 5.0 kcal/mole and −21 cal/degree per mole, respectively (25 °C). These values are close to the corresponding changes in ferric haemoproteins and differ substantially from those in Fe 3+ . The significance of this result is discussed.

Inhibition of the Fe3+H2O2 reaction by acetone

Abstract The inhibition of the Fe 3+ + H 2 O 2 reaction by acetone is of the competitive type. Under the conditions of the experiments no complex is formed between acetone and Fe 3+ . The results have been interpreted, in terms of Kremer and Steins scheme, as indicating a binding of the secondary Fe 3+ H 2 O 2 complex by acetone. From the results it appears that one acetone molecule can bind on the average, nine molecules of the secondary complex.

Decomposition of H2O2 by haemin. Inhibition of the reaction by azide

Abstract 1. 1. NaN 3 inhibits the haemin-catalysed decomposition of H 2 O 2 . The inhibition is of the competitive type. Haemin itself does not combine with azide. 2. 2. The results are in agreement with a mechanism in which the formation of two intermediate complexes between haemin and H 2 O 2 is assumed. Inhibition occurs by a reversible combination of azide with the secondary haemin-H 2 O 2 complex. 3. 3. The inhibition is not complete. The catalyst-substrate-inhibitor complex still possesses some residual activity. 4. 4. Increased affinity for azide in the presence of H 2 O 2 has also been observed in catalase. The analogous behavior towards azide may indicate a basic similarity of the catalytic mechanism in the two systems.