Reactivity of the horseradish peroxidase compounds I and II toward organometallic substrates. A stopped-flow kinetic study of oxidation of ferrocenes.
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.
Goral
V N
VN
Department of Chemistry, Moscow State University, Russia.
Ryabov
A D
AD
D002384:Catalysis; D005296:Ferrous Compounds / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D000075163:Metallocenes; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013379:Substrate Specificity
D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; C098326:oxyferryl porphyrin pi cation radical; C032949:ferrocenecarboxylic acid; C083053:dimethylaminomethylferrocene; D006735:Horseradish Peroxidase