The reaction mechanism of plant peroxidases
Longu, S.; Medda, R.; Padiglia, A.; Pedersen, J.Z.; Floris, G.
Italian Journal of Biochemistry 53(1): 41-45
2004
ISSN/ISBN: 0021-2938 PMID: 15356961 Document Number: 573852
The catalysis of class III plant peroxidases is described based on the reaction scheme of horseradish peroxidase. The mechanism consists in four distinct steps: (a) binding of peroxide to the heme-Fe(III) to form a very unstable peroxide complex, Compound 0; (b) oxidation of the iron to generate Compound I, a ferryl species with a pi-cation radical in the porphyrin ring; (c) reduction of Compound I by one substrate molecule to produce a substrate radical and another ferryl species, Compound II; (d) reduction of Compound II by a second substrate molecute to release a second substrate radical and regenerate the native enzyme. Under unfavourable conditions some inactive enzyme species can be formed, known as dead-end species. Two calcium ions are normally found in plant peroxidases and appear to be important for the catalytic efficiency.