| Popis: |
The oxidative function of peroxidases has long been of interest to chemists and biochemists because of the unstable and highly oxidized states that are reversibly assumed by the heme active site during the catalytic cycle. Features of the various peroxidase mechanisms have been postulated to occur in the catalytic cycles of other important heme enzymes such as cytochrome oxidase and cytochrome P-450. Peroxidases are widespread in plants but are also found in numerous animal tissues. An extensively studied peroxidase which is isolated from horseradish root is the main topic of this paper. The catalytic sequence of horseradish peroxidase involves two oxidative intermediates known as compounds I and II (Dunford, 1982), (Dawson, 1988). Compound I, two oxidation equivalents above the resting enzyme, contains a ferryl heme with an additional electron removed from the porphyrin ring, forming a porphyrin π-cation radical (Dolphin and Felton, 1974), (McMurry and Groves, 1986). Compound II, which contains an oxo-ferryl heme, results from the reduction of compound I which restores an electron to the porphyrin ring (Hewson and Hager, 1979). |
