Lipoxygenase product specificity

Starfish oocytes rapidly converted radiolabelled AA into lipoxygenase products, specifically 8-hydroxyeicosatetraenoic acid [70]. Subsequent work showed that oocyte maturation is induced in a stereospecific way by (8/ )-hydroxy-eicosatetraenoic acid [71]. Again, the authors concluded that this compound is involved in transducing the oocyte maturation hormone signal at the plasma membrane level. 

GRF-stimulated GH release is also inhibited by lipoxygenase inhibitors, suggesting participation of some lipoxygenase product(s). However, in this area of research more work is also required to attribute a specific messenger role to these arachidonic acid metabolites. 

Among these enzymes, lipoxygenase and hydroperoxide lyase seem to be of the most importance, since product specificity of lipoxyge-... 

Enzymes of this type were formerly known as fat oxidase, carotene oxidase, and lipoxidase lipoxydase in French) and have also been listed under E.C. 1.99.2.1 and E.C. 1.13.1.13. It should be emphasized that several species of enzyme, distinguishable by substrate and product specificities as well as by physical properties, are covered by the generic term lipoxygenase. ... 

The regiospecificity of the lipoxygenase product formation depends on the positional specificity of both the initial hydrogen abstraction and the subsequent dioxygen attachment. The formation of the different regioisomeric lipoxygenase products from linoleic acid can be explained by a simple reverse orientation... 

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. 

Lipid oxidation in subcellular fractions can be mediated by enzyme systems in muscle microsomes that maintain iron in the ferrous form by reduced nicotinamide adenine dinucleotide (NADH). However, this redox system may not be enzymatic because, unlike lipoxygenase, no specific lipid oxidation products have been identified. Ascorbate and other reducing agents may have the same effects in the presence of heme-protein complexes. On the other hand, the presence of 15-lipoxygenase in chicken muscle may be responsible for oxidative deteriorations in uncooked chicken meat during frozen storage. Phospholipases... 

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. 

Product specificity of tea chloroplast lipoxygenase was examined using llnolelc acid, methyl llnoleate and llnoleyl alcohol (as the substrate). 

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). 

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