Fatty acids allene oxide synthase

Allene oxide synthase route. Allene oxide synthase dehydrates hydroperoxides, affording allene oxide fatty acids, Allene oxides are rapidly hydrolyzed into ketols [2,6]. Allene oxide, corresponding to 13-HPOT, along with hydrolysis undergoes cyclization, affording cyclopentenone 12-oxo-10,15(Z)-phytodienoic acid. The last upon its reduction and j8-oxidation is converted into jasmonic acid ... 

SONG, W.C., FUNK, C.D., BRASH, A.R., Molecular cloning of an allene oxide synthase A cytochrome P450 specialized for the metabolism of fatty acid hydroperoxides, Proc. Natl. Acad. Sci. USA, 1993, 90, 8519-8523. 

FROELICH, J.E., ITOH, A., HOWE, G.A., Tomato allene oxide synthase and fatty acid hydroperoxide lyase, two cytochrome P450s involved in oxylipin metabolism, are targeted to different membranes of chloroplast envelope., Plant Physiol., 2001,125,306-317. 

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Howe, G.A., G.I. Lee, A. Itoh, L. Li, and A.E. DeRocher (2000). Cytochrome P450-depend-ent metabolism of oxylipids in tomato. Cloning and expression of allene oxide synthase and fatty acid hydroperoxide lyase. Plant Physiol. 123, 711-724. 

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. 

Fig. 8. Metabolism of 18 3 fatty acid to oxylipins. I. Lipoxygenase 2, alleneoxide synthase 3, allene oxide cyclase 4, 12-oxo-phytodienoic acid reductase, -oxidation 5, hydroperoxide lyase.

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