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Reactivity of horseradish peroxidase compounds I and II (HRP-I and HRP-II) toward organometallicic substrates, viz water-soluble ferrocenes RFc (R = COOH and CH2NMe2), has been studied at 25 degrees C, pH 6.0 and ionic strength 0.1 M. The second-order rate constants k2 for the reaction of HRP-I with FcCOOH and FcCH2NMe2 equal (1.00 +/- 0.04) x 10(6) and (0.27 +/- 0.01) x 10(6) M-1 s-1, respectively. The values of k3 for the reaction of HRP-II with FcCOOH and FcCH2NMe2 equal (1.1 +/- 0.1) x 10(4) and (0.25 +/- 0.01) x 10(4) M-1 s-1, respectively. The steady-state kinetic study of the HRP-catalyzed oxidation of the ferrocenes by H2O2 under the same conditions gave the second-order rate constants of (0.94 +/- 0.03) x 10(4) and (0.24 +/- 0.06) x 10(4) M-1 s-1 for FcCOOH and FcCH2NMe2, respectively, which are in a good agreement with k3. The results reported here confirm the proposal that the rate-limiting step of the steady-state oxidation of ferrocenes is the electron transfer from the substrate to HRP-II.

The rate constants for the H2O2-induced irreversible inactivation (kinact) of chloroperoxidase from Caldariomyces fumago evaluated from the analysis of complete kinetic curves of chlorination or bromination of monochlorodimedon were found to follow the rate law kinact = k[H2O2]/(K + [H2O2]) with k = 0.009 > or = 0.002 and 0.0095 > or = 0.010 s-1 and K = (13 > or = 4) x 10(-3) and (9 > or = 2) x 10(-3) M in the presence of 0.01 M chloride and bromide, respectively, at pH 2.75 and 25 degrees C. The data show that chloroperoxidase investigated is more than by a factor of 10 less resistant toward hydrogen peroxide compared to horseradish peroxidase. The possible reason for it and the biotechnological implications are briefly discussed.

The ferricenium salt FcH+BF4- behaves as a specific substrate of glucose oxidase acting instead of dioxygen with the effective parameters of the Michaelis-Menten equation kcat = 2.60 x 10(2) s-1 and KM = 2.7 x 10(-4) M at 25 degrees C, pH 6.8 and [D-glucose] = 0.001 M. The activity of glucose oxidase can easily be monitored by conventional UV-vis spectrophotometry at 617 nm following the bleaching of the ferricenium dye.