Hydroperoxide lyase, mechanism

Fatty acid hydroperoxide lyase is one of the enzymes responsible for volatile Cft- and C9-aldehyde formation from linoleic and linolenic acid. This enzyme cleaves 9- and/or 13-hydroperoxides derived from linoleic and linolenic acid. The enzyme is distributed in a wide range of plant species in membrane bound forms both chloroplastic and non-chloroplastic. Three types of hydroperoxide lyases have been reported 9-hydroperoxide-specific, 13-hydroperoxide-specific and nonspecific. Other properties of the hydroperoxide lyase including substrate specificity and reaction mechanism are discussed in this review. 

The origin of oxygen in cleavage products-Cl and XIII) of the hydroperoxide lyase reaction presumably occurs in a manner (Fig. 4) similar to the mechanism for acid-catalyzed rearrangement of the 13-... 

Hydroperoxide lyases catalyse the cleavage of the C-C single bond that is adjacent to the peroxy group. In the case of 13-HpOTrE, the C-12-C-13 bond is cleaved, yielding an unsaturated aldehyde and (9 )-12-oxo-9-dodecenoic acid, which is a precursor of the wound hormone traumatin (Scheme 10). The volatile aldehydes formed via the peroxide lyase pathway exhibit bactericidal properties and are emitted by plants in response to wounding. Thus they may be regarded as part of the plant s disease resistance mechanisms [53]. 

Figure 3.61 Mechanism of action of hydroperoxide lyases to 9-hydroperoxides of fatty acids.

Fig. 3.31. Mechanism of the cleavage of hydroperoxides by lyases (according to Wurzenberger and Grosch, 1986) a in plants, b in mushrooms...

Oxylipins are commonly found metabolites in higher plants and most of them originate from polyunsaturated fatty acid hydroperoxides by enzymatic transformations which have been extensively studied (for recent reviews, see 1,2). Two well characterized enzymes a lyase and an allene oxide synthase were shown to degrade hydroperoxides into compounds of physiological importance since they can ultimately yield fragrances or plant hormones such as jasmonic acid. We have recently reported a new fate for fatty acid hydroperoxides the peroxygenase pathway. It involves two enzyme activities i.e. a peroxygenase and an epoxide hydrolase which lead to the formation of epoxidized fatty acids and their derived dihydrodiols which are relevant to plant defense mechanisms. 

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