Possible Mechanism of Oxygen Activation in Linoleate Peroxidation by Fusarium Lipoxygenase

Abstract

The Oxygen activating mechanism of Fusarium lipoxygenase, a heme-containing dioxyge-nase, was studied. The enzyme did not require any cofactors, such as H₂O₂, however, both superoxide disniutase and catalase inhibited linoleate peroxidation by Fusarium lipoxygenase. A low concentration of H₂O₂ caused a distinct acceleration in enzymatic peroxidation. These results indicate that both O₂^- and H₂O₂ are produced as essential intermediates of oxygen activation during formation of linoleate hydroperoxides by Fusarium lipoxygenase, This peroxidation reaction was also prevented by scavengers of singlet oxygen (¹O₂), but not by scavengers of hydroxyl radical (OH•). Generation of O₂ in the enzyme reaction was detected by its ability to oxidize epinephrine to adrenochrome. Moreover, the rate of peroxide forma-tion was greater in the D₂O than in the H₂O buffer system. These results suggest that the Haber-Weiss reaction (O₂^-+H₂O₂→OOH^-+OH•+¹O₂) is taking part in linoleate peroxida-tion by Fusarium lipoxygenase, and the ¹O₂ evolved could be responsible for the peroxidation of linoleate. H₂O₂ produced endogenously in the enzyme reaction might act as an activating factor for the enzyme. This possible mechanism of oxygen activation can explain the absence of a need for exogenous cofactors with Fusarium lipoxygenase in contrast to an other home-containing dioxygenase, tryptophan pyrrolase, which requires an exogenous activating factor, such as H₂O₂.