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Abstract ▼ AI-Helper

Lipoxygenase (EC 1.13.11.12) from rice bran was studied to elucidate its catalytic reaction mechanism for the hydroperoxidation. This enzyme showed a very limited substrate specificity toward a series of free fatty acids having more than two isolated double bonds which have cis configuration. Metal ...

Lipoxygenase (EC 1.13.11.12) from rice bran was studied to elucidate its catalytic reaction mechanism for the hydroperoxidation. This enzyme showed a very limited substrate specificity toward a series of free fatty acids having more than two isolated double bonds which have cis configuration. Metal chelating agents such as EDTA and o-phenanthroline showed a significant loss of the enzyme activity although the addition of exogeneous bivalent metal ions including magnesium, manganese, zinc and iron, etc. showed no effect on the ezyme activity. In addition, the enzyme was not affected by the treatment with diisopropylfluorophosphate and N-ethylmaleimide, but the photooxidation of the enzyme with methylene blue resulted in a marked loss of the enzyme activity. The pK values of the enzyme were estimated to be about 6.4 and 7.3, while the enzyme-substrate complex showed only one ionization at pH 5.9. Electronparamagnetic resonance spectrum for the free enzyme indicates the presence of a trivalent iron in the molecule, and its analysis during the hydroperoxidation suggests the valence state of iron is changed into divalent by the interaction with the substrate. Based on the nature of non-heme iron in the enzyme molecule, we proposed a model mechanism of the rice bran lipoxygenase catalyzed reaction.