Protection by different agents against inactivation of lipoxygenase by hydrogen peroxide.

H2O2 is a potent inactivator of lipoxygenase. In this paper, the ability of different agents [mannitol, oleic, stearic and linoleic acid, n-butanol, and hydroperoxy octadecadienoic acid (HPOD)] to prevent the inactivation of tomato lipoxygenase by hydrogen peroxide has been studied. The involvement of OH' in the inactivation process is suggested by the ability of mannitol to prevent the loss of activity. This radical would be produced by reaction of H2O2 with the Fe(II) lipoxygenase. The most effective protection was displayed by HPOD, the product of the reaction of lipoxygenase with linoleic acid. This result could be explained by the conversion of the native enzyme into the Fe(III) lipoxygenase in the presence of HPOD; the Fe(III) enzyme is not able to react with H2O2 and no OH' will be produced. The protective effect obtained with oleic and stearic acid could be explained by an occupation of the active center by these inhibitors. The enzyme would not transform them, but their presence would hamper the conversion of H2O2 in OH' and limit the damage in the active center.