Microsomes, enzymatic lipid peroxidation

Musgrave ME, Gould SP, Ablett RF (1987) Enzymatic lipid peroxidation in the gonadal and hepatopancreatic microsomal fraction of cultivated mussels Mytilus edulis L.). J Food Sci 52 609-612... 

This mechanism is now considered to be of importance for the protection of LDL against oxidation stress, Chapter 25.) The antioxidant effect of ubiquinones on lipid peroxidation was first shown in 1980 [237]. In 1987 Solaini et al. [238] showed that the depletion of beef heart mitochondria from ubiquinone enhanced the iron adriamycin-initiated lipid peroxidation whereas the reincorporation of ubiquinone in mitochondria depressed lipid peroxidation. It was concluded that ubiquinone is able to protect mitochondria against the prooxidant effect of adriamycin. Inhibition of in vitro and in vivo liposomal, microsomal, and mitochondrial lipid peroxidation has also been shown in studies by Beyer [239] and Frei et al. [240]. Later on, it was suggested that ubihydroquinones inhibit lipid peroxidation only in cooperation with vitamin E [241]. However, simultaneous presence of ubihydroquinone and vitamin E apparently is not always necessary [242], although the synergistic interaction of these antioxidants may take place (see below). It has been shown that the enzymatic reduction of ubiquinones to ubihydroquinones is catalyzed by NADH-dependent plasma membrane reductase and NADPH-dependent cytosolic ubiquinone reductase [243,244]. 

Antioxidant activity was also tested in a liver microsome system. In this study, mice were treated by oral intubation (2 times/wk) with 0.2 ml olive oil alone or containing CLA (0.1 ml), linoleic acid (0.1 ml), or dl-a-tocopherol (lOmg). Four weeks after the first treatment, liver microsomes were prepared and subsequently subjected to oxidative stress using a non-enzymatic iron-dependent lipid peroxidation system. Microsomal lipid peroxidation was measured as thiobarbituric acid-reactive substance (TBARS) production using malondialdehyde as the standard. It was found that pretreatment of mice with CLA or dl-a-tocopherol significantly decreased TBARS formation in mouse liver microsomes (p < 0.05) (Sword, J. T. and M. W. Pariza, University of Wisconsin, unpublished data). 

It is well established that liver microsomes in the presence of NADPH and in the absence of chelator are capable of oxidizing cholesterol and other 3P-hydroxy 5-unsaturated steroids yielding the common autoxidation products 3-8 [16]. In this case, the cholesterol oxidation is secondary to the enzymatic NADPH-dependent lipid peroxidations. The enzyme-catalyzed reaction is required, however, merely to reduce Fe i to Fe which in turn catalyzes ordinary autoxidation. It has also been shown by EPR studies using spin traps that radicals are involved in these conversions [16]. The major radicals detected were lipid peroxyl radicals and superoxide, whereas only small amounts of hydroxyl radicals were... 

Poulson R (1976) The enzymatic conversion of protoporphyrinogen IX to protoporphyrin IX in mammalian mitochondria. J Biol Chem 251 3730-3733 Quinlan GJ, Halliwell B, Moorhouse CP, Gutteridge JMC (1988) Action of lead and aluminum ions on iron-stimulated lipid peroxidation in liposomes, erythrocytes and rat liver microsomal fractions. Biochim Biophys Acta 962 196-200... 

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