Lipoxygenase secondary products

Lipoxygenase (linoleate oxygen oxidoreductase) catalyzes the hydroperoxidation of fatty acids containing a methylene-interrupted conjugated diene system. The degradation of the hydroperoxides results in the formation of numerous secondary products (46-48). 

Formation of Secondary Products and Lipohydroperoxide Destruction. As early as 1945 Holman and Burr (132) found that crude soybean lipoxygenase acting on a number of substrates produced carbonyl-containing material in addition to diene. Holman, as noted above (107), used his crystalline enzyme and found that it was difficult to establish a correspondence between O2 consumption and diene conjugation. The diene concentration always tended to be too low. Privett et al. 123) found that the reaction products varied with enzyme concentration and method of addition. Vioque and Holman 133) identified 9-keto-ll,13- and 13-keto-9,ll-octadecadienoate with the usual hydroperoxides in a reaction carried out with linoleic acid and a relatively large amount of crude soybean lipoxygenase at pH 9. 

Lipohydroperoxide Destruction and Secondary Products. Investigators have noted that during a lipoxygenase reaction the hydroperoxide concentration, as measured with Fe(CNS)2, rises and then declines [e.g., Balls et al (15), Blain and Barr 137), Gini and Koch (138)]. This phenomenon has been attributed to a lipohydroperoxide-destroying enzyme, or lipohydroperoxidase, as well as to hematin compounds (3, 143), However Pistorius and Axelrod reproduced this phenomenon with crystalline lipoxygenase-1 (139). There is little doubt that the anaerobic destruction of lipohydroperoxide, as detailed by Garssen et al 134), is responsible for this. 

Unsaturated fatty acid hydroperoxides are rather unstable and may be rapidly converted via enzymic and non-enzymic pathways into a complex pattern of secondary products, some of which exhibit interesting biological activities [5,6]. In plants, 13S-HpOTrE is one of the most important fatty acid hydroperoxides formed by lipoxygenases [53] and this compound is further metabolized via several types of enzymic reactions (Scheme 10). 

This enzyme oxidizes linoleic and linolenic acids rapidly in whole flour or milling products containing wheat germ or bran mixed with water. The initial hydroperoxides formed by lipoxygenases in stored wheat bran are converted to secondary products, mono- and trihydroxy fatty acids. These oxidation products causing bitter and rancid flavors are formed in higher concentrations in hydrated products than in dry raw materials. Rancid flavors develop rapidly on hydration. 

Hydroperoxides of linoleic and Hnolenic acids also react with sensitive food components, such as carotenes, to form colourless products (lipoxygenase, however, do not directly catalyse the decomposition of carotenes) and induce oxidative changes in sulfur amino acids and proteins. Secondary products of lipid oxidation initiate radical reactions of proteins that lead to a reduction in their nutritional value. 

Huneck S, Yoshimura I (1996) Identification of lichen substances. Springer, Berlin, p 493 Hussain MS, Fareed S, Ansari S et al (2012) Current approaches toward production of secondary plant metabolites. J Pharm Bioallied Sci 4 10-20 Ingolfsdottir K, Gudmundsdottir GF (2002) Effects of tenuiorin and methyl orsellinate from the lichen Peltigera leucophlebia on 5-/15-lipoxygenases and proliferation of malignant cell lines in-vitro. Phytomedicine 9 654-658... 

Saturated and unsaturated hydrocarbons with odd and even numbers of carbon atoms in the molecule (about C11-C35) are present as the primary substances in all vegetable oils and animal fats. Alkanes, alkenes, alkadienes and alkatrienes also arise as oxidation products of unsaturated fatty acids, catalysed by lipoxygenases or by autoxidation of fatty acids during food storage and processing. Only the lower hydrocarbons can play a role as odour-active substances. The main hydrocarbons resulting from oxidation of unsaturated fatty acids are ethane from Hnolenic acid, pentane and butane from Hnoleic acid and hexane and octane from oleic acid. The immediate precursors of hydrocarbons are the fatty acid hydroperoxides (Table 8.4). The unsaturated hydrocarbons are predominantly (Z)-isomers. Numerous other hydrocarbons, including ahcycHc hydrocarbons, appear as secondary hpid oxidation products. 

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