Lipoxygenase substrate specificity

Of the 8 fatty acids tested as giganteum lipoxygenase substrates (delta 9,12-octadecadienoic, delta 9,12,15-octadecatrienoic, delta 6,9,12-octadecatrienoic, delta 11,14-elcosadienoic, delta 8,11,14-eicosatrienoic, delta 5,8,11,14-eicosatetraenoic, delta 5,8,11,14,17-eicosapentaenoic, and delta 4,7,10,13,16,19-docosahexaenoic acids, all-cis), only arachidonlc (C-20 4), eicosapentaenoic (C-20 5) and docosahexaenoic (C-22 6) acids were consistently metabolized (Table 1). It is noteworthy that the C-18 compounds apparently are not suitable substrates for the giganteum enz5nne under the incubation conditions used. If this initial observation is verified by work in progress, this will be the first documented instance of such selective lipoxygenase substrate specificity. 

Applications of peroxide formation are underrepresented in chiral synthetic chemistry, most likely owing to the limited stability of such intermediates. Lipoxygenases, as prototype biocatalysts for such reactions, display rather limited substrate specificity. However, interesting functionalizations at allylic positions of unsaturated fatty acids can be realized in high regio- and stereoselectivity, when the enzymatic oxidation is coupled to a chemical or enzymatic reduction process. While early work focused on derivatives of arachidonic acid chemical modifications to the carboxylate moiety are possible, provided that a sufficiently hydrophilic functionality remained. By means of this strategy, chiral diendiols are accessible after hydroperoxide reduction (Scheme 9.12) [103,104]. 

Major products of the lipoxygenase reaction are 9- and 13-hydroperoxides of IV and V, VI, VII, VIII and IX. Hydroperoxide lyase utilizes the 9- and/or 13-hydroperoxides (VI, VII, VIII and IX). Based on substrate specificity, hydroperoxide lyase is classified into three types. The first type is 9-hydroperoxide-specific. 

Gillmor, S.A., Villasenor, A., Fletterick, R., Sigal, E., Browner, M.F. 1997. The structure of mammalian 15-lipoxygenase reveals similarity to the lipases and the determinants of substrate specificity. Nat. Struct. Biol. 4 1003-1009. 

The AS bond appears to be of Importance for activity, perhaps due to enzymic substrate specificity, leading to a more metabollcally active compound. Such enzymic modification could be due to lipoxygenase or cyclooxygenase activity, which Is discussed In the final section of this review. 

The enzymic formation of aldehydes, ketones, alcohols, and oxoacids (from linoleic and linolenic acids) on disruption of plant tissues is an important biosynthetic pathway by which fruit and vegetable volatiles are formed. Some examples are (E)-2-hexenal ("leaf aldehyde") and ( )-3-hexenol ("leaf alcohol") in tea (E)-2-hexenal in apples (E,Z)-2,6-nonadienal ("violet Teaf aldehyde") and (E)-2-nonenal in cucumber ( Z)-5-nonenal in musk melon (Z,Z) -3,6-nonadienol in water melon, and 1-octen-3-ol ("mushroom alcohol") in certain edible mushrooms and Fungi. The enzyme system is highly substrate specific to a (Z,Z)-1,4-pentadiene system (like lipoxygenase) splitting the >C = C< double bond at the W - 6 and/or W - 9 position. Therefore linoleic-, linolenic-, and arachidonic acids are natural substrates. It seems to be a common principle in leaves, fruits, vegetables, and basidiomycetes. 

Figure 5 shows a reaction scheme which may explain the formation of Cg- and C-] 2-components in leaves and fruits. Hatanaka et al. (12) proposed a cleaving system operative in Thea sinensis leaves and other plants which is located in the chloroplasts. E2 shows a similar substrate specifity as lipoxygenase E-. The enzymic breakdown products from linolenic acid are ( )-3-hexenal (I) and 12-oxo-( )-9-dodecenoic acid (V). Both constituents are transformed into the corresponding ( )-2-enals by E3 and/or by chemical reactions. During these transformation the carbonyls may be reduced to alcohols by alcohol oxidoreductase E4. In ripe fruits the right pathway E-j, E2f E3 seems to become operative. 

Wecksler, A. T., V. Kenyon et al. 2008. Substrate specificity changes for human reticulocyte and epithelial 15-lipoxygenases reveal allosteric product regulation. 

Holman et al (1969) studied the substrate specificity of soybean lipoxygenase. Linoleic acid had the highest activity but other acids with a double bond at C-13 (n—6) were also active. The hydrophobic interaction of the pentadiene system with the enzyme appeared to be more important than the carbonyl group. 

The 12-lipoxygenase and 15-lipoxygenase have been identified in fish gill tissue and in chicken muscle by their production of 12-hydroperoxide and 15-hydroperoxide from arachidonic acid and other polyunsaturated fatty acids in fish. TTie substrate dependency and product specificity toward other long-chain polyunsaturated fatty acids in fish (20 5 n-3, 22 4 n-6, 22 5 n-3) indicate that the 12-lipoxygenase is specific towards the methyl rather than the carboxyl end and can be described as an n-9 lipoxygenase. The hydroperoxides produced by these enzymes may be decomposed in the presence of metal catalysts to form volatile carbonyls that cause off-flavors in fish and frozen chicken meat. 

EXPRESSION AND SUBSTRATE SPECIFICITY OF LIPOXYGENASE ISOENZYMES EMBRYOS OF GERMINATING BARLEY... 

Lipoxygenase activity was measured spectrophotometrically as described by Doderer et al. 11] or, in the case of substrate specificity studies, polarographically by following the oxygen consumption using a Clark-type electrode. 

SUBSTRATE SPECIFICITY OF BARLEY LIPOXYGENASE ISOENZYMES Purification oflox-1 and lox-2... 

Expression and Substrate Specificity of Lipoxygenase Isozymes from Embryos of Germinating Barley. 

Important. The substrate specificities and the product specificities of these enzymes determine the composition of volatile aldehydes formed from llnolelc acid and llnolenlc acid. The present report describes occurrence of, and substrate and product specificities of, lipoxygenase and hydroperoxide lyase In leaves, particularly In tea leaves. 

Table 1 Substrate specificity of lipoxygenase and Cs-aldehyde-forming activity... 

Verification of the presence of lipoxygenase enzyme(s) in L. giganteum and preliminary characterization of their substrate specificities are presented in the following report. 

Table 1. Substrate Specificity of Lagenidium giganteum Lipoxygenase...

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