Hydroperoxides hydroperoxide lyase

METABOLISM OF FATTY ACID HYDROPEROXIDES Hydroperoxide Lyase... 

R-HETE is a very potent and selective inducer of oocyte maturation [196, 199]. 8S-HETE does not show this activity. The allene oxide hydrolysis products and the hydroperoxide lyase products were not active in promoting oocyte maturation [200]. 

In plant tissues, various enzymes convert the hydroperoxides produced by LOX to other products, some of which are important as flavor compounds. These enzymes include hydroperoxide lyase, which catalyzes the formation of aldehydes and oxo acids hydroperoxide-dependent peroxygenase and epoxygenase, which catalyze the formation of epoxy and hydroxy fatty acids, and hydroperoxide isomerase, which catalyzes the formation of epoxyhydroxy fatty acids and trihydroxy fatty acids. LOX produces flavor volatiles similar to those produced during autoxidation, although the relative proportions of the products may vary widely, depending on the specificity of the enzyme and the reaction conditions. 

Figure 8.6 A diagram of the oxylipin pathway. LOX lipoxygenase AOS allene oxide synthase HPL hydroperoxide lyase AOC allene oxide cyclase OPDA Reductase 12-oxo-phytodienoic acid-10,11-reductase.

MATSUI, K., SHIBUTANI, M., HASE, T., KAJIWARA, T., Bell pepper fruit fatty acid hydroperoxide lyase is a cytochrome P450 (CYP75B) in many plant tissues, FEBS Lett., 1996, 394,21-24. 

MATSUI, K., WILKINSON, J., HIATT, B., KNAUF, V., KAJIWARA, T., Molecular cloning and expression of Arabidopsis fatty acid hydroperoxide lyase, Plant Cell Physiol., 1999,40,477-481. 

The volatiles produced by the LOX pathway and autoxidation are typically volatile aldehydes and alcohols responsible for fresh and green sensorial notes. In the LOX pathway these volatile compounds are produced in response to stress, during ripening or after damage of the plant tissue. The pathway is illustrated in Scheme 7.2. Precursors of the LOX (EC 1.13.11.12) catalysed reactions are Cis-polyunsaturated fatty acids with a (Z,Z)-l,4-pentadiene moiety such as linoleic and a-linolenic acids that are typically oxidised into 9-, 10- or 13-hydro-peroxides depending on the specificity of the LOX catalyst. These compounds are then cleaved by hydroperoxide lyase (HPL) into mainly C, C9 and Cio aldehydes, which can then be reduced into the corresponding alcohols by alcohol dehydrogenase (ADH EC 1.1.1.1) (Scheme 7.2) [21, 22]. The production of volatile compounds by the LOX pathway depends, however, on the plants as they have different sets of enzymes, pH in the cells, fatty acid composition of cell walls, etc. 

Scheme 7.2 Pathway for the enzymatic degradation of linoleic acid and linolenic acid via the lipoxygenase (LOX) pathway to Ce key aroma compounds in fruits and vegetables responsible for green notes. HPL hydroperoxide lyase, ADH alcohol dehydrogenase...

Oxidative cleavage of unsaturated fatty acids by lipoxygenase and hydroperoxide lyase... 

In nature, the green notes are produced after the destruction of the plants tissue (leaves, fruits or vegetables). Destruction of the cell wall leads to a cascade of enzyme-catalysed reactions polyunsaturated fatty acids with the diene system described before are converted into hydroperoxides by LOX catalysis. The hydroperoxide lyase cleaves the hydroperoxides in the whole cascade, oxireduc-tases are involved too. The biotechnological large-scale production of natural green notes follows the natural pathway. 

At present, there are some patents concerning the production of green notes by recombinant guava 13-hydroperoxide lyase expressed in Escherichia coli [70, 71] and Cucumis melo hydroperoxide lyase the latter yields a mixture of C6 and C9 compounds [72]. 

Hexenol ( leaf alcohol ) Linolenic acid Soy lipoxygenase + plant hydroperoxide lyase + baker s yeast 4 g kg 5-101 year (also by isolation from plant oils) Addition of baker s yeast to obtain the alcohol without yeast the aldehyde is the major product [60, 66]... 

Scheme 233 Formation of aliphatic flavour aldehydes and alcohols, a Biotechnological reaction sequence mimicking plant biosynthesis of C6 compounds (green notes ), b HomologoiK reaction sequence in fimgi leading to mushroom-like C8 compounds. The stoichiometric formation of w-oxo-carboxylic acids during hydroperoxide lyase cleavage is not depicted...

The cloning, characterisation and expression of many lipoxygenase (TOX) [17] and hydroperoxide lyase (HPL) [18] genes has led researchers to propose new processes for the production of green note flavours. HPT specifically produces the highly demanded compound ds-3-hexenal from the 13-hydroperoxide of linolenic acid and hexanal from the hydroperoxide of linoleic acid, both of which are formed by TOXs (Scheme 26.2). 

Scheme 26.2 Short-chain aldehyde formation by lipoxygenases and hydroperoxide lyases...

FIGURE 7.6 Short-chain aldehydes and alcohols produced from the degradation of fatty acids in grapes via the lipoxygenase (LOX)/hydroperoxide lyase (HPL) pathway during the prefermentative stages of vinification (adapted from Camara, 2004). 

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. 

Figure 10-20) these are changed into cis unsaturated aldehydes by hydroperoxide lyase. The cis unsaturated aldehydes are transformed by isomerase into the corresponding trans isomers. These same substances in another matrix would be experienced as off-flavors. The use of lipoxygenase as a versatile biocatalyst has been described by Gardner (1996). 

The formation of Cg aldehyde and alcohols in plant tissues is related to cell destruction. Disruption of intact cells during crushing and milling results in the release of lipid-degrading en2ymes, lipoxygenases and fatty acid hydroperoxide lyase, which cleave the fatty acid moiety to Cg... 

Hatanaka, A., Kajiwara, T, and Matsui, K. Reaction Specificity of Lipoxygenase and Hydroperoxide Lyase. In Progress in Flavour Precursor Studies (Schreier, P. and Winterhalter, P, eds.). Allured Puplishing, pp.151-170 (1993)... 

Homostaj, A.R. and Robinson, D.S., Purification of hydroperoxide lyase from cucumbers, Food Chem., 66, 173, 1999. 

Noordermeer, M.A. et al., Characterization of three cloned and expressed 13-hydroperoxide lyase isoenzymes from alfalfa with unusual N-terminal sequences and different enzyme kinetics, Eur. J. Biochem., 267, 2473, 2000. 

Rehbock, B., Ganber, D., and Berger, R.G., Efficient generation of 2E-hexenal by a hydroperoxide lyase from mung bean seedlings, Food Chem., 63, 161, 1998. 

Riley, J.C.M., Willemot, C., and Thompson, J.E., Lipoxygenase and hydroperoxide lyase activities in ripening tomato fruit, Postharvest Biol. Tech., 7, 97, 1996. 

Tijet, N. et al., Purification, molecular cloning and expression of the gene encoding fatty acid 13-hydroperoxide lyase from guava fruit (Psidium guajava), Lipid, 35, 709, 2000. 

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