Lipoxygenase indicator enzyme

Specificity for the site of O2 insertion into the substrate is also a property of the enzyme although it can be infiuenced by experimental conditions. In autoxidation of linoleic acid it was known that a mixture of 9- and 13-hydroperoxides was formed (113). Values for the positional specificity for soybean lipoxygenase indicate a wide variation. Dolev et al. 114) found exclusive formation of 13-hydroperoxide. Other values for the ratio of 13- to 9-hydroperoxide are 95 5 by Eriksson and Leu... 

Application of Kinetic Data to Thermal Processing. In most studies on ttiermal inactivation of indicator enzymes including peroxidase, lipoxygenase, and LAHase, reaction rate constants and thermodynamic parameters have been determined on the assumption that thermal inactivation of the enzymes follows first order reaction kinetics (22). However, a deviation from first order kinetics is generally observed fipm the residual activity curve. This deviation has been explained by several mechanisms, including the formation of enzyme aggregate with different heat stabilities, the presence of heat stable and labile enzymes, and the series type inactivation kinetics. 

As previously indicated, four enzymes related to the enzymatic degradation of polyphenols, polyphenoloxidase, peroxidase, laccase, and lipoxygenase, are extensively reviewed in this chapter. The first enzyme described is polyphenoloxidase. 

These results indicate that the Fusarium lipoxygenase differs from the soybean lipoxygenase in various respects soybean lipoxygenase is a nonheme iron-containing dioxygenase and has a molecular weight of 102,000, optimum pH of 6.5 to 7,0 and isoelectric point of pH 5.4. The soybean enzyme is not inhibited by cyanide and catalyzes the peroxidation of linoleic acid and linolenic acid at equal rates74-76,193. ... 

Lipoxygenases, of which the enzyme from soy beans has been studied the most, also catalyze oxidation of polyunsaturated fatty acids in lipids as indicated in Eq. 21-17. Formation of the hydroperoxide product is accompanied by a shift of the double bond and conversion from cis to trans configuration. Soybean lipoxygenase is a member of a family of related lipoxygenases that are found in all eukaryotes. All... 

Leukotriene biosynthesis. The asterisks indicate that both the lipoxygenase and dehydrase reactions are driven by the single enzyme 5-lipoxygenase. (GGTP, > -glutamy 1 transpeptidase.)... 

Besides 12-LOX in platelets, the 5-LOX isoforms are constitutive in neutrophils. Evidences indicate that LOXs are involved in inflammation diseases and in atherosclerosis. 5-LOX is the enzyme that catalyzes the formation of leukotrienes with potential role for leukocytes and platelets interaction and inflammation. After platelet and leukocyte stimulation, products of both COX-1 and 5-LOX pathways increase. COX-1 activity derivatives increase the vascular permeability mediated by prostaglandins and produce platelet aggregation mediated by TXA2. The product of the lipoxygenase pathway, 5-oxo-6,8,1 1,14-eicosatetraenoic acid (5-Oxo-ETE), induces leukocyte chemotaxis and inflammation. 5-Oxo-ETE is formed by the oxidation of 5S-hydroxy-ETE (5-HETE) by 5-hydroxyeicosanoid dehydrogenase (5-HEDH), a microsomal enzyme found in leukocytes and platelets (42). 

Chemical and Physical Properties. Too little is known about the physical properties of pure lipoxygenases to permit their comparison. The separation of isoenzymes during their isolation and their diflFerential behavior in electrophoresis indicate the existence of different enzymes. However characterization of the enzymes through their enzymatic properties shows that the lipoxygenases comprise a large group of diverse enzymes. 

Experiments using the UV-visible spectrophotometer at 25°C gave results in accord with the ESR studies. When lipoxygenase was titrated with enzyme-generated 13-l hydroperoxide under anaerobic conditions, the absorption at 360 nm increased to a plateau. Addition of linoleic acid abolished the increase at 360 nm. These results indicate that the structure responsible for the signal at g = 6 is also responsible for the increase in absorption at 360 nm. 

Although both primary H/T and D/T isotope effects were measured as a function of temperature, the focus of the interpretation was on primary D/T isotope effects, since the smaller commitment for D- than H-transfer leads to a more complete contribution of the chemical step to the measured parameters (see e.g. Section 10.21). The results obtained from this study [92], as well as the earlier work [91], indicate a striking trend in which the value of Ad /At moves from near unity to below unity as the surface of the protein is modified (either by glycosylation or addition of polyethylene glycol). A similar type of pattern has been seen in other enzyme systems, such as the thermophilic ADH [24] (Section 10.5.1.1) and soybean lipoxygenase (SLO) [43] (see Section 10.5.3.1 below) where modification of reaction conditions away from either optimal temperature (ht-ADH) or optimal protein packing (via... 

Fig. 12. Metabolism of arachidonic acid by cytochrome P-450 enzymes and the formation of three structurally distinct metabolite families.

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