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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
biochemistry, genetics and molecular biology
Hemes and Hemoproteins. 5: Kinetics of the Peroxidatic Activity of Microperoxidase-8: Model for the Peroxidase Enzymes
Journal of Inorganic Biochemistry, Volume 30, No. 3, Year 1987
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Description
The peroxidatic activity of the heme octapeptide from cytochrome c, microperoxidase-8 (MP-8), was assayed at 25°C under conditions where formation of Compound I is rate limiting. In the pH range 6-9, the reaction rate increased linearly with a slope close to unity. The active form of the substrate is the hydroperoxide anion, HO2-, and an extrapolated second-order rate constant was obtained for the reaction of aquoMP-8 with HO2- of 3.7 × 108 M1̄ sec-1, which is close to the second-order rate constants reported for reaction of the peroxidase enzymes with H2O2. Comparison with published data shows that the Fe3+ ion of MP-8 reacts as expected with simple anions, electrons, and HO2-, while the analogous reactions of the enzymes all show a requirement for one H +. We conclude that the peroxidase enzymes activate H2O2 under physiological conditions through a pH-independent, H+-coupled binding of the required H2O2-. The peroxidase activity of MP-8 can be increased more than tenfold by the presence of the guanidinium ion, which is ascribed to formation of the ion-pair GuaH+HO2-; this suggests a role for the invariant distal Arg in the enzymes. © 1987.
Authors & Co-Authors
Baldwin, David A.
South Africa, Johannesburg
University of the Witwatersrand
Marques, Helder M.
South Africa, Johannesburg
University of the Witwatersrand
Pratt, John M.
South Africa, Johannesburg
University of the Witwatersrand
Statistics
Citations: 98
Authors: 3
Affiliations: 1
Identifiers
Doi:
10.1016/0162-0134(87)80064-8
ISSN:
01620134