The inactivation and catalytic pathways of horseradish peroxidase with m-chloroperoxybenzoic acid. A spectrophotometric and transient kinetic study
The kinetics of the catalytic cycle and irreversible inactivation of horseradish peroxidase C (HRP-C) reacting with m-chloroperoxybenzoic acid (mCPBA) have been studied by conventional and stopped-flow spectrophotometry. mCPBA oxidized HRP-C to compound I with a second order-rate constant k1 = 3.6 X...
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Veröffentlicht in: | The Journal of biological chemistry 1997-02, Vol.272 (9), p.5469 |
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Sprache: | eng |
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Zusammenfassung: | The kinetics of the catalytic cycle and irreversible inactivation of horseradish peroxidase C (HRP-C) reacting with m-chloroperoxybenzoic acid (mCPBA) have been studied by conventional and stopped-flow spectrophotometry. mCPBA oxidized HRP-C to compound I with a second order-rate constant k1 = 3.6 X 10(7) m-1 s-1 at pH 7.0, 25 degrees C. Excess mCPBA subsequently acted as a one-electron reducing substrate, converting compound I to compound II and compound II to resting, ferric enzyme. In both of these reactions, spectrally distinct, transient forms of the enzyme were observed (lambda(max) = 411 nm, epsilon = 45 mM-1 cm-1 for compound I with mCPBA, and lambda(max) = 408 nm, epsilon = 77 mM-1 cm-1 for compound II with mCPBA). The compound I-mCPBA intermediate (shown by near infrared spectroscopy to be identical to P965) decayed either to compound II in a catalytic cycle (k3 = 6.4 X 10(-3) s-1) or, in a competing inactivation reaction, to verdohemoprotein (ki = 3.3 X 10(-3) s-1). Thus, a partition ratio of r = 2 is obtained for the inactivation of ferric HRP-C by mCPBA. The intermediate formed from compound II with mCPBA is not part of the inactivation pathway and only decays via the catalytic cycle to give resting, ferric enzyme (k5 = 1.0 X10(-3) s-1). The data are compared with those from earlier steady-state kinetic studies and demonstrate the importance of single turn-over experiments. The results are discussed in terms of the physiologically relevant reactions of plant peroxidases with hydrogen peroxide |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.272.9.5469 |