Mechanisms of catalase activity of heme peroxidases.
In the absence of exogenous electron donors monofunctional heme peroxidases can slowly degrade hydrogen peroxide following a mechanism different from monofunctional catalases. This pseudo-catalase cycle involves several redox intermediates including Compounds I, II and III, hydrogen peroxide reduction and oxidation reactions as well as release of both dioxygen and superoxide. The rate of decay of oxyferrous complex determines the rate-limiting step and the enzymes' resistance to inactivation. Homologous bifunctional catalase-peroxidases (KatGs) are unique in having both a peroxidase and high hydrogen dismutation activity without inhibition reactions. It is demonstrated that KatGs follow a similar reaction pathway as monofunctional peroxidases, but use a unique post-translational distal modification (Met+-Tyr-Trp adduct) in close vicinity to the heme as radical site that enhances turnover of oxyferrous heme and avoids release of superoxide. Similarities and differences between monofunctional peroxidases and bifunctional KatGs are discussed and mechanisms of pseudo-catalase activity are proposed.
Vlasits
Jutta
J
Department of Chemistry, Division of Biochemistry, BOKU-University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
Jakopitsch
Christa
C
Bernroitner
Margit
M
Zamocky
Marcel
M
Furtmüller
Paul G
PG
Obinger
Christian
C
D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D002374:Catalase / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006801:Humans; D010544:Peroxidases / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism
D001426:Bacterial Proteins; D005656:Fungal Proteins; D010940:Plant Proteins; D006418:Heme; D010544:Peroxidases; D002374:Catalase