Lipoxygenase reaction products

Furthermore, in the system with coupled lipase and lipoxygenase, the production rate of HP is governed by the first enzymatic reaction and mass transfer. When TL,- is small (0 to 1 mM equiv. 3 mM LA), the kinetic curve has a sigmoid shape due to surface active properties of LA and HP [25]. Hydrolysis of TL and the increase of LA favor the transfer of LA. Such a transfer allows the lipoxygenase reaction to progress. Since lipox-ygenation consumes LA and produces HP, catalysis and transfer demonstrates a reciprocal influence. 

Monoamine oxidase, tyrosine hydroxylase, and L-amino acid oxidase generate hydrogen peroxide as their reaction product. Hydrogen peroxide is also produced by auto-oxidation of catecholamines in the presence of vitamin C. Moreover, phospholipase A2 (PLA2), cyclooxygenase (COX), and lipoxygenase (LOX), the enzymes associated with arachidonic acid release and the arachidonic acid cascade,... 

Privett et al 123) made an important discovery in elucidating the structure of the products of the lipoxygenase reaction. They established... 

Smith and Lands have also shown that the lipoxygenase reaction is accompanied by reaction inactivation of the enzyme. The reaction rate is characteristic for each substrate and increases with the extent of unsaturation. They postulate that the enzyme has two sites—one for the substrate and one for the product hydroperoxide. They proposed a highly speculative mechanism in which the hydroperoxide combines with O2 to... 

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. 

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. 

Wheat lipoxygenase and soybean lipoxygenase, catalyzing oxidation of fatty acids, generate oxidized reaction products that improve the dough-forming properties and baking performance of flour. A similar role is performed by polyphenol oxidase and peroxidase. 

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. 

HETE was the first product shown to arise from a lipoxygenase reaction of arachidonic acid in mammalian systems. Chronologically it was also the first lipoxygenase product to be synthesized. As outlined in Scheme 4.8, Corey et al. ° carried out a stereospecific total synthesis from acetonide alcohol 21 which... 

Hamberg, M., C. Su, and E. Oliw, Manganese Lipoxygenase. Discovery of a his-Allylic Hydroperoxide as Product and Intermediate in a Lipoxygenase Reaction, /. Biol. Chem. 273 13080-13088 (1998). 

An obvious way to find out about the physiological function of an enzyme is to study the fate of the products that result from the reaction catalysed by the enzyme. The primary products of the lipoxygenase reaction, fatty-acid hydroperoxides, are potentially dangerous and should be quickly metabolized. Two major routes for metabolizing lipoxygenase products have been identified, collectively known as the lipoxygenase pathway [176]. This was recently extended by the discovery of the peroxygenase cascade [177]. 

Lipoxygenases have been isolated from two species in the imperfect genus Fusarium (Anamorpic Hypocreaceae, 4.C1.15). Initially, LOX activity from a variety of Fusarium species was assayed and Fusarium oxysporum found to be the most active [19]. The LOX from F. oxysporum was crystallized and its reaction products characterized [20]. As is common for plant LOX, the positional specificity was pH dependent. Incubations at pH 9 resulted in a 70 30 ratio of 9-HPODE to 13-HPODE while incubations at pH 12 decreased the ratio to 56 44 [20]. There were two pH optima, at 6 and 10, and the enzyme showed a 10 1 preference for... 

The biological function of a lipoxygenase is closely connected with the type of the reaction catalysed and with the kind of reaction product formed. From a biological point of view, it appears to be reasonable to classify the reactions of lipoxygenases in two groups (Table 1), i.e. those with free polyenoic fatty acids as substrate and those with more complex substrates in which the polyenoic fatty acid is esterified. As far as the reactions with free polyenoic fatty acids are concerned, owing to their abundance linoleic and a-linolenic acids are the most relevant... 

The next analytical challenge will be the characterization of possible lipoxygenase and cyclooxygenase reaction products of CLA and its metabolites, to verify the existence of a direct interaction between CLA and eicosanoid formation. 

Hydroperoxy fatty acids as such cannot be separated by GC as they decompose at high temperatures, and HPLC is probabiy the preferred method for their anaiysis [168], Nonetheiess, there are times when it is advantageous to convert them to the hydroxy derivatives by means of sodium borohydride reduction and then to the TMS ethers for GC anaiysis, for exampie for identification by GC-mass spectrometry products derived from linoleic [223,341,911,946,1005], arachidonic [124,407,568, 1005] and docosahexaenoic acids [948] have been examined in this way (the list is not intended to be comprehensive). Woollard and Mallet [1005], in particular, have presented a comprehensive list of ECL data for compounds of this type. In addition, GC methods were used for the determination of the absolute configuration of hydroperoxides formed by lipoxygenase reaction [124,568,947]. 

The oxygenation of the allylic ketones. Direct evidence for such type of lipoxygenase reaction was obtained in 1991 independently by ourselves [4] and by German group [5]. The last one incubated an allyUc ketone, prepared by oxidation of ricinoleic acid, with soybean LOX. They have identified an a,jS-unsaturated 7-diketone as the predominant product. Studying the oxidation of a-ketols, we have suggested, that the primary products of their LOX oxidation are the corresponding hydroperoxides [4]. 

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