Lipoxygenase self-inactivation

Although for many years lipoxygenase activity in fish was discounted (14-17), plant lipoxygenases were easily demonstrated, and became well-accepted. Research into the biosynthesis of the six-, eight-, and nine-carbon volatile aroma compounds of mushrooms (27, 56) and cucumber/melon-fruits (37, 57-58) showed the concerted activities of both site-specific lipoxygenases and hydroperoxide lyases. Because animal lipoxygenases exhibit self-inactivation properties (59-60), early experimentation failed to detect an active lipoxygenase from fish, and this led to conclusions that autoxidation was responsible for the... 

The relative ratios of alcohols and carbonyls for the six-, eight- and nine-carbon volatiles in fish (23-24) and oysters (26) parallel those encountered in cucumber fruits (37) and mushrooms (27, 56) if the two systems are combined. Therefore, the use of plant-based enzyme systems for the controlled generation of fresh seafood flavors and aromas has been under consideration in our laboratory as a means to overcome some of the self-inactivating problems associated with fish lipoxygenases. 

It has been reported that a single methionine residue of rabbit reticulocyte 15-lipoxygenase can be oxidized to its sulphoxide by treatment of the enzyme with 13-hydroperoxy-octadecadienoic acid (a 15-lipoxygenase product from linoleic acid) under anaerobic conditions [59]. Since under this condition the enzyme functioned as lipohydroperoxidase , splitting the hydroperoxide, and resulted in self-inactivation , a central role of the methionine residue was presumed for the catalysis of the enzyme. Recently, this particular methionine has been identified as Met-590 in human 15-lipoxygenase and as Met-591 in rabbit 15-lipoxygenase. When Met-590 in the human enzyme is replaced by leucine by the site-directed mutagenesis, the mutant enzyme is still inactivated by 13-hydroperoxyoctadeca-dienoic acid, 15-HpETE or AA. The result shows that the enzyme inactivation is not attributable to methionine oxidation [60]. 

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