Lipoxygenases (LOXs)

Lipoxygenases (LOXs)

Lipoxygenases are abundant enzymes that have been identified in numerous cells including platelets, leukocytes, and vascular and neural tissue. Because of possessing regiospecificity during interaction, lipoxygenases have been designated as arachidonate 5-, 8, 12-, 15-lipoxygenase (5-LOX, 8-LOX, 12-LOX, and 15-LOX). Typically, the same HETE isomer can be produced by several distinct lipoxygenaseisoforms.

Lipoxygenase (LOXs) is an enzyme that accelerates the oxygenation of polyunsaturated fatty acids. Lipoxygenases are non-heme, iron containing dioxygenases that catalyze the regio- and stereo-specific insertion of molecular oxygen into polyunsaturated lipids containing lZ-4Z-pentadiene systems producing conjugated hydroperoxide products. LOXs are ubiquitous in plants and animals and have been discovered in fungi and two bacterial species. The non-heme iron cofactor is coordinated by a highly conserved set of three histidines, an asparagine, the carboxyl group of the C-terminal isoleucine and a water molecule.

Lipoxygenases (LOX) constitute a large gene family of non-heme iron containing fatty acid dioxygenases, which are commonly found in plants and animals. Therefore it can be inhibited by iron chelators or redox active compounds. However, the chelators or redox active compounds is non-specific and consequently may result in undesirable side effects. In order to obtain lipoxygenase specific inhibitor, more structure information for the lipoxygenase family is required. Currently, there are no human 5-LOX structures that provide a model for how the substrate, arachidonic acid (AA) binds in the LOX active site, a model critical for the development of LOX specific inhibitors. The strict region-specificity of the various lipoxygenases indicates that targeting of a single LOX isozyme is feasible, a requisite feature of an effective therapeutic strategy. Predicating the bind site of 8R-LOX helps understand how arachidonic acid interacts with LOX structures and thus help developing LOX specific inhibitors. There is a 8R-LOX: AA complex model proposed by Neau, but this proposed model has not been verified.

Lipoxygenase's function in plants has been connected to flavor and odor formation of fruits. In animals, this enzyme forms precursors for chemical messengers such as leukotrienes or lipoxins. Mercier and Gélinas investigated slightly oxidized fats and long dough mixing times to replace the use of benzoyl peroxide for the flour bleaching process. Oxygen intake by dough can be accelerated in the presence of polyunsaturated fatty acids (i.e. linolenic and linoleic acids) that have unconjugated double bonds. Supplementing dough with linoleic acid has been shown to accelerate pigment discoloration. Oils high in linoleic acid (sunflower) versus those low (colza) were more effective in bleaching dough after being oxidized for 6-10 hours. Mercier and Gélinas (2001) found that free linoleic acid and highly oxidized sunflower oil have major dough bleaching potential, especially in combination with long dough mixing times. Unfortunately, this was proven under intense mixing conditions that can be too long for standard or commercial dough development. While the process of oxidizing oils high in polyunsaturated fatty acids appears ideal, this process has only been tested in the dough stage. Effects of bleaching on distillers grains are yet unknown. Perhaps this is a process that can result in improved color and be completed at bakeries.

A bleaching effect has also been accomplished when 1-2% of an enzymeactivated soy flour, pea flour, or broad bean flour was utilized. It was important to note that these mixtures will not necessarily produce lighter colored flour, rather a whiter breadcrumb upon baking. The addition of soy flour also improved the nutritional value of the overall product due to its high levels of the amino acids lysine and tryptophan. Another study involved altering carotenoids in corn gluten meal (CGM) with soy flour (5%) as a lipoxygenase source. Results revealed that 65% of the carotenoids were bleached at a pH of 6.5, compared to only 47% bleached at a pH of 5.0. The ideal pH range for carotenoid reduction of CGM was 6.5-7.0. Higher mechanical energy for stirring optimized bleaching while decreasing reaction time needed to achieve maximum bleaching. The use of enzyme-activated flour produced a reaction that could be suitable for distillers grains.


Saunders, Jessica A. "Analysis of physical, chemical, and functionality properties of distillers dried grains with solubles (DDGS) for use in human foods." (2008).

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