Figure 1.
Mechanism of peroxidase-catalyzed ROS production. (A) Hourglass model which summarizes the inter-conversions among active and inactive forms of peroxidases involved in ROS generation. This model emphasizes that 2 distinct cycles are initiated by conversion of native peroxidase with e− acceptor via conventional peroxidase cycle or with e− donor via oxygenase-like cycle. (B) Graph theoretical summary of redox state shifts in plant peroxidase upon treatment with various substrates or chemicals. Each of small graphs is consisted with 5 vertices corresponding to the enzyme intermediates at different redox states, and directed edges (maximally 6 edges allowed). The formal oxidation states of the heme within the enzyme are indicated by numbers in the circles (vertices). Directed edges (arrows) indicate the transitions of the redox states. Red and blue edges represent the steps with and without direct and/or concomitant release of O2•−. Final states of the enzyme following various chemical treatments are highlighted with red circle. Graphs in (B) were made based on the documented knowledge (Kawano, 2003a, 2003b, 2013; Kawano et al., 1998, 2001, 2002a, 2002b, 2004; Kawano and Bouteau, 2013a; Kawano and Muto, 2000; Kimura et al., 2014; Takayama et al., 2012). (C) Expanded model for SA-induced oxidative burst, based on the relay of H2O2-independnet and H2O2-dependent peroxidase actions. Series of reactions were numbered from (1) to (8).