Lipoxygenases lipid oxidation

Kanner, J., Harel, S. and Granit, R (1992). Nitric oxide, an inhibitor of lipid oxidation by lipoxygenase cyclooxygenase and hemoglobin. Lipids 27, 46—49. 

Lipoxygenases catalyze oxidation of polyunsaturated fatty acids in plant lipids. Within animal tissues the lipoxygenase-catalyzed reaction of arachidonic acid with 02 is the first step in formation of Ieukotrienes and other mediators of inflammation. These reactions are discussed in Chapter 21. 

Radical oxidation chains are initiated when LOOH is decomposed to initiating LO and OH radicals by light and heat, to LO /LOO by metals, or to LO by the enzyme itself (120). Very low levels produced in plant or animal tissues may provide the invisible initiators that make lipid oxidation sometimes appear spontaneous. Perhaps just as important, LOOH produced by lipoxygenase can accumulate to relatively high levels under appropriate conditions (e.g., cold and dark, as in frozen unblanched materials), then lead to a cascade of rapid oxidation when LOOH decomposes. 

Peroxide value is the measure of reactive oxygen content of a fat in terms of milliequivalents per 1000-g fat, following AOCS method Cd 8-53 or AOAC Method 965.33 (109). Elevated peroxide values indicate that lipid oxidation has taken place (110). Free fatty acids can serve as substrates for lipoxygenase and peroxidase (111), both of which are inactivated during heating (112). Once the cell... 

The effects of berbamine, oxyacanthine, and berberine on 5-lipoxygenase lipid peroxidation in phospholipid liposomes induced by 2,2 -azo-(bis-2-amidinopropane)(AAPH), deoxyribose degradation, and their reactivities against the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) were studied. None of the alkaloids showed any appreciable effects in the inhibition of 5-lipoxygenase. Reactivity against DPPH increased in the following order berberine < oxyacanthine < berbamine. Pro-oxidant effects of the alkaloids were excluded, since deoxyribose degradation was not influenced as determined by the release of malondialdehyde [200],... 

Fats or raw materials that serve as a source for fatty acids are frequently employed in process flavourings. During the flavour reaction, thermal peroxidation of lipids such as triglycerides, fatty acids and phospholipids occurs. This non-enzymatic lipid oxidation, also called autoxidation, leads to a very complex mixture of reaction products, and has to be regarded separately from the enzymatic lipid oxidation which occurs at low temperature and is catalysed by lipoxygenases. 

Lipids in foods can be oxidized by both enzymatic and nonenzymatic mechanisms. One of the enzymes that is considered important in lipid oxidation is lipoxygenase, which has recognition for its off-flavor development in vegetables and... 

The destruction of p-carotene during lipid peroxidation is readily observed by bleaching of the carotene color (44). Presumably, p-carotene oxidation is initiated by H-abstraction, and such a mechanism has been proposed for the cooxidation of carotenoids during the lipoxygenase catalyzed oxidation of polyunsaturated fatty acids (45), as shown by Reaction Q. 

LOX-catalyzed lipid oxidation differs from the free radical reaction by the formation of hydroperoxides at a certain position of the chain of, most often, a free FA. Lipoxygenases use molecular oxygen to catalyze the stereo- and regiospecific oxygenation of PUFA with -cisA- dY-pentadiene moieties. LOX react enzymat-... 

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