Electron transport microsomal

Peroxisomes are found in many tissues, including liver. They are rich in oxidases and in catalase, Thus, the enzymes that produce H2O2 are grouped with the enzyme that destroys it. However, mitochondrial and microsomal electron transport systems as well as xanthine oxidase must be considered as additional sources of H2O2. 

Figure 11-5. Electron transport chain in microsomes. Cyanide (CN ) inhibits the indicated step.

Pederson, T.C., Buege, J.A. and Aust, S.D. (1973). Microsomal electron transport. The role of reduced nicotinamide dinucleotide phosphateliver microsomal lipid peroxidation. J. Biol. Chem. 248, 7134—7141. 

J. Aranda, S. MacLeod, K. Renton, and N. Eade, Hepatic microsomal drug oxidation and electron transport in newborn infants, J. Pediatr, 85, 534 (1974). 

Pawar SS, Kachole MS. 1978. Hepatic and renal microsomal electron transport reactions in endrin treated female guinea pigs. Bull Environ Contam Toxicol 20 199-205. 

The desaturation process is particularly interesting as it provides an example of a microsomal (as opposed to mitochondrial) electron transport system. The enzymes responsible, fatty acyl-CoA desaturases, are examples of mixed function oxidases... 

Garfinkel, D A comparative study of electron transport in microsomes. Comp. Biochem. Physiol. (1963) Q, 367-379-... 

Chan, T.M., Gillett, J.W. and Terriere, L.C. Interaction between microsomal electron transport systems of trout and male rat in cyclodiene epoxidation. Comp. Biochem. Physiol. (1967), 20, 731-7 +2. 

Starek A, Plewka A, Kaminski M, et al. 1988. [The effect of kerosene hydrocarbons and phenobarbital on the microsomal electron transport chain in rat liver.] Folia Med Cracov 29(l-2) 49-57. (Polish)... 

A close dependence of the activity of UDP-glucuronyltransferase (A12, G3), glucose-6-phosphatase and enzymes related to microsomal electron transport to NADPH (W6), on the structural integrity of the... 

Two examples of toxicity, where the target is known, are carbon monoxide, which interacts specifically with hemoglobin, and cyanide, which interacts specifically with the enzyme cytochrome a3 of the electron transport chain (see chap. 7). The toxic effects of these two compounds are a direct result of these interactions and, it is assumed, depend on the number of molecules of the toxic compound bound to the receptors. However, the final toxic effects involve cellular damage and death and also depend on other factors. Other examples where specific receptors are known to be involved in the mediation of toxic effects are microsomal enzyme inducers, organophosphorus compounds, and peroxisomal proliferators (see chaps. 5-7). 

Microsomal reduction of chromium(VI) can also result in the formation of chromium(V), which involves a one-electron transfer from the microsomal electron-transport cytochrome P450 system in rats. The chromium(V) complexes are characterized as labile and reactive. These chromium(V) intermediates persist for 1 hour in vitro, making them likely to interact with deoxyribonucleic acid (DNA), which may eventually lead to cancer (Jennette 1982). Because chromium(V) complexes are labile and reactive, detection of chromium(V) after in vivo exposure to chromium(VI) was difficult in the past. More recently, Liu et al. (1994) have demonstrated that chromium(V) is formed in vivo by using low-frequency electron paramagnetic resonance (EPR) spectroscopy on whole mice. In mice injected with sodium dichromate(VI) intravenously into the tail vein, maximum levels of chromium(V) were detected within 10 minutes and declined slowly with a life time of about 37 minutes. The time to reach peak in vivo levels of chromium(V) decreased in a linear manner as the administered dose levels of sodium... 

Garcia J, Jennette K. 1981. Electron-transport cytochrome P-450 system is involved in the microsomal metabolism of the carcinogen chromate. J Inorganic Biochem 14 281-295. 

Benveniste, I., Gabriac, B., Fonne, R., Reichhart, D., Salauen, J.P., Simon, A., and Durst, F., Higher plant cytochrome P-450 microsomal electron transport and xenobiotic oxidation, Dev. Biochem., 23, 201-208, 1982. 

The major source is the activity of the mitochondria and microsomal electron transport chains. The 4-electron reduction of oxygen to water, of course, is the normal process underlying mitochondrial electron transport ... 

It is generally accepted that liver microsomes contain two electron transport systems each containing a flavoprotein reductase. The paths of electron flow can be outlined as follows ... 

Vitamin E deficiency is also associated with impaired mitochondrial oxidative metabolism and impaired activity of microsomal cytochrome P450-dependent mixed-function oxidases, and hence the metabolism of xenobi-ofics. There is no evidence that vitamin E has any specific role in electron transport in mitochondria or microsomes. Again, changes in membrane lipids and oxidative damage presumably account for the observed metabolic abnormalities. 

The second initiation way for the lipoperoxidation in the organism can be defined as semi-enzymatic or quasi-enzymatic. During this mechanism the O " radicals are generated by enzymes including NAD(P)H-dependent oxidases of mitochondrial and microsomal electron transport chaines, NADPH-dependent oxidase of phagocytes, xanthine oxidase and other flavine oxidases. After the HO formation the oxidation process develops in non-enzymatic way. 

Scheme 1. Hepatic microsomal electron transport for drug oxidation and...

Table I. Effect of Deficiency on Electron Transport Components and Drug Enzymes in Guinea Pig Liver Microsomes...

Sies H (1978) The use of perfusion ofliver and other organs for the study of microsomal electron-transport and cytochrome P-450 systems. Methods Enzymol 52 48-59... 

Binder, R.L. and JJ. Stegeman. Microsomal electron transport and xenobiotic monooxygenase activities during the embryonic period of development in the killifish Fundulus heteroclitus. Toxicol. Appl. 

---