Reactions of the Class II Peroxidases, Lignin Peroxidase andArthromyces ramosus Peroxidase, with Hydrogen Peroxide

Abstract

The reactions of the fungal enzymes Arthromyces ramosus peroxidase (ARP) and Phanerochaete chrysos- porium lignin peroxidase (LiP) with hydrogen peroxide (H2O2) have been studied. Both enzymes exhibited cata- lase activity with hyperbolic H2O2 concentration de- pendence (Km ⬇ 8–10 mM, kcat ⬇ 1–3 sⴚ1). The catalase and peroxidase activities of LiP were inhibited within 10 min and those of ARP in 1 h. The inactivation con- stants were calculated using two independent methods; LiP, ki ⬇ 19 ⴛ 10ⴚ3 sⴚ1; ARP, ki ⬇ 1.6 ⴛ 10ⴚ3 sⴚ1. Com- pound III (oxyperoxidase) was detected as the majority species after the addition of H2O2 to LiP or ARP, and its formation was accompanied by loss of enzyme activity. A reaction scheme is presented which rationalizes the turnover and inactivation of LiP and ARP with H2O2.A similar model is applicable to horseradish peroxidase. The scheme links catalase and compound III forming catalytic pathways and inactivation at the level of the [compound I䡠H2O2] complex. Inactivation does not occur from compound III. All peroxidases studied to date are sensitive to inactivation by H2O2, and it is suggested that the model will be generally applicable to peroxi- dases of the plant, fungal, and prokaryotic superfamily. Peroxidases