Ethylene enhances reactivity of superoxide with peroxidase to form the oxy-ferrous complex

Ethylene and its analogues acetylene, carbon monoxide, and propylene inhibited the rate of oxidation of indole-3-acetic acid by peroxidase. Annulment of this effect by addition of superoxide dismutase showed that inhibition occurred only in the presence of the superoxide anion radical (O2-.). Kinetic and spectral data established that ethylene and its analogues enhanced markedly the rate of reaction of O2-. with peroxidase. This reaction resulted in the formation of compound III, an oxy-ferrous complex of peroxidase. In the presence of indole-3-acetic acid, the interaction between ethylene, peroxidase, and O2-. activated the reduced peroxidase in equilibrium compound III shuttle. O2-. is a major product of this shuttle, and compound III constitutes the dominant steady-state form of peroxidase. These interactions may help to explain the mechanism of action of ethylene as a plant growth regulator.