Bleaching of Dichlorophenolindophenol by a Coupled Oxidation with Linoleate Catalyzed by Soybean Lipoxygenase

Abstract

The coupled bleaching of 2, 6-dichlorophenolindophenol by soybean lipoxygenase-1, was found to occur only under anaerobic conditions with a characteristic lag phase quite unlike the wellknown induction phase associated with lipoxygenase-catalyzed oxidation of linoleate hydroperoxide (LOOH)-free linolelic acid. The duration of this distinctive lag phase was very sensitive to lipoxygenase concentrations and equalled the length of time required for the primary enzyme activity to render the reaction solution virtually anaerobic. The onset of bleaching was marked by a gradual build-up of a ketodiene presumably derived from LOOH. Singlet O₂ and superoxide anion did not appear to be involved in the enzymecatalyzed bleaching while the xanthine-xanthine oxidase system known to produce O₂^- was effective in bleaching DCPIP. It is proposed that the bleaching reaction was a result of an oxidative and irreversible alteration of DCPIP involving a number of reactive oxidants known to be produced anaerobically upon incubation of LOOH and linoleic acid with native lipoxygenase.