Manganese peroxidase from the lignin-degrading basidiomycete Phanerochaete chrysosporium: Transient state kinetics and reaction mechanism
- Oregon Graduate Center, Beaverton (United States)
- Univ. of Alberta, Edmonton (Canada)
Stopped-flow techniques were used to investigate the kinetics of the formation of manganese peroxidase compound I (MnPI) and of the reactions of MnPI and manganese peroxidase compound II (MnPII) with p-cresol and Mn{sup II}. All of the rate data were obtained from single turnover experiments under pseudo-first order conditions. In the presence of H{sub 2}O{sub 2} the formation of MnPI is independent of pH over the range 3.12-8.29 with a second-order rate constant of (2.0{+-}0.1) {times} 10{sup 6} M{sup {minus}1} s{sup {minus}1}. The activation energy for MnPI formation is 20 kJ mol{sup {minus}1}. MnPI formation also occurs with organic peroxides such as peracetic acid, m-chloroperoxybenzoic acid, and p-nitroperoxybenzoic acid with second-order rate constants of 9.7 x 10{sup 5}, 9.5 {times} 10{sup 4}, and 5.9 {times} 10{sup 4} M{sup {minus}1} s{sup {minus}1}, respectively. The reactions of MnPI and MnPII with p-cresol strictly obeyed second-order kinetics. The second-order rate constant for the reaction of MnPII with p-cresol is extremely low, (9.5{+-}0.5) m{sup {minus}1} s{sup {minus}1}. Kinetic analysis of the reaction of Mn{sup II} with MnPI and MnPII showed a binding interaction with the oxidized enzymes which led to saturation kinetics. The first-order dissociation rate constants for the reaction of Mn{sup II} with MnPI and MnPII are (0.7{+-}0.1) and (0.14{+-}0.01) s{sup {minus}1}, respectively, when the reaction is conducted in lactate buffer. Rate constants are considerably lower when the reactions are conducted in succinate buffer. Single turnover experiments confirmed that Mn{sup II} serves as an obligatory substrate for MnPII and that both oxidized forms of the enzyme form productive complexes with Mn{sup II}. Finally, these results suggest the {alpha}-hydroxy acids such as lactate facilitate the dissociation of Mn{sup II} from the enzyme.
- OSTI ID:
- 5623894
- Journal Information:
- Journal of Biological Chemistry; (United States), Vol. 264:6; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FUNGI
BIOCHEMISTRY
PEROXIDASES
BIOCHEMICAL REACTION KINETICS
CRESOLS
HYDROGEN PEROXIDE
MANGANESE COMPLEXES
PH VALUE
SUBSTRATES
AROMATICS
CHEMISTRY
COMPLEXES
ENZYMES
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
KINETICS
ORGANIC COMPOUNDS
OXIDOREDUCTASES
OXYGEN COMPOUNDS
PEROXIDES
PHENOLS
PLANTS
PROTEINS
REACTION KINETICS
TRANSITION ELEMENT COMPLEXES
550200* - Biochemistry