Microsomes electron transport

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. 

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. 

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. 

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... 

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... 

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 ... 

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...

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. 

One molecule of oxygen accepts two pairs of electrons, one from palmitoyl-CoA and the other from NADPH or NADH. The electrons NAD(P)H are transported via cytochrome-bs reductase to cytochrome bs (microsomal electron transport Chapter 14). An enzyme-bound superoxide radical is responsible for the oxidation of acyl-CoA. Four desaturases specific for introducing cis double bonds at C9, Ca, C5, and C4, respectively, are known. If the substrate is saturated, the first double bond introduced is C9. With an unsaturated substrate, other double bonds are introduced between the carboxyl group and the double bond nearest the carboxyl group. Desaturation yields a divinylmethane arrangement of double bonds (—CH=CH—CH2—CH=CH—). Usually desaturation alternates with chain elongation. Desaturation is inhibited by fasting and diabetes. The oxidation of unsaturated fatty acids occurs in mitochondria. 

Heme oxygenase, which catalyzes the conversion of free heme groups to biliverdin and CO, functions as part of a microsomal electron transport system similar to that of cytochrome 1 450-(FP = NADPH-cytochrome P450 reductase.) Heme oxygenase requires 3 02 and 5 NADPH. Biliverdin reductase can use NADPH or NADH as a reductant. 

Many type b cytochromes associated with the classic cytochrome oxidase (a and 03) show their a peaks at 561-563 nm, and they are usually designated as cytochrome b. The name cytochrome 61 was originally used for the pigments with a peak at 557-560 nm, but it is now generally applied to the cytochrome in the nitrate reductase system. Cytochrome 62 (a, 557 nm) is the entity of yeast lactate dehydrogenase which contains FMN and protoheme. Cytochromes 63 (a, 559 nm) and 65 (a, 556 nm) participate in the microsomal electron transport system in plants and animals, respectively. Both the primary and ternary structures of cytochrome 65 are known. Cytochromes bg (a, 563 nm) and 6-559 are the components of the photosynthetic electron transport system in plant. 

Plants contain type b cytochromes participating in photosynthetic electron transport systems in addition to those in mitochondrial and microsomal electron transport systems. There is some confusion about the names of these cytochromes 231). Several type b cytochromes, including photosynthetic h-559 and b and microsomal 6-555, have been highly purified and fairly well characterized. The last one is described in Section III (see Table IV). 

Reactive oxygen species are known to play important roles in many biochemical reactions that maintain normal cell functions. These species are produced as normal intermediates in mitochondrial and microsomal electron-transport systems, and some enzymes that produce substantial amounts of O2 or H2O2 have been identified in several parasites (5). 

T. cruzi contains NADPH-cytochrome c reductase activity in both the microsomal and cytosolic-cell fractions (29). The cytosolic enzyme may act as an oxygenase, protecting the cell in times of hydrogen peroxide production, since trypanosomes are deficient in catalase (30). It may also metabolize drugs directly, possible conferring resistance to antitrypanosomal drugs (31). The particulate enzyme form probably functions in microsomal electron transport associated with trypanosomal cytochrome P450. 

Moreover, a great source of H2O2 production in the intact cell appears to be generated by the autooxidation of chemically reactive compounds during reductive processes associated with the mitochondrial and microsomal electron transport systems and during action of SOD (Chance et al., 1979 Forman and Boveris, 1982). 

Schacter, B.A., E.B. Nelson, H.S. Marver, and B.S. Masters (1972). Immunochemical evidence for an association of heme oxygenase with the microsomal electron transport system. J. Biol. Chem. 247, 3601-3607. 

Fig. 6. Mitochondrial and microsomal electron transport for cytochrome P450-dcpendent monooxygenases...

Chromium(V) was detected in incubation mixtures of chromate with microsomes and NADPH l EPR signals characteristic of Cr(V) appeared within 20 s after initiation of the reaction and persisted for 80 min. The rapid formation of Cr(V) in this system implies that a direct one-electron transfer from the microsomal-electron-transport cytochrome P-450 system to chromate is a likely step in the mechanism of reduction. 

Soni M, Nomiyama H, Nomiyama K. 1990. Chronic inhalation effects of tetrachloroethylene on hepatic and renal microsomal electron transport components and 6-aminolevulinic acid dehydratase in rats. Toxicology Letters 54 207-213. 

Staudinger, H., Krisch, K.. and Leonhauser. S. Role of ascorbic acid in microsomal electron transport and the possible relationship to hydrox-ylation reactions. Ann. N. Y. Acad. Sci., 92. 195-207.1961. 

Hrycay EG, O Brien PJ (1973) Microsomal electron transport. 1. Reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase and cytochrome P-450 as electron carriers in microsomal NADPH-peroxidase activity. Arch Biochem Biophys 157 7-22... 

Difference spectroscopy showed that the extract contained the hemo-proteins P-450 and cytochrome 65. Of special interest is the inhibition of 6 -hydroxylase activity by CO and the reversal of this inhibition by light, suggesting that P-450 may be involved in the reaction. In a subsequent experiment, the 6,.3-hydroxylase activity was assayed in the presence and absence of CO, and under light of various wavelengths between 400-500 m//. Reactivation of the CO inhibited enzyme was maximum at 450 mix. An action spectrum obtained from these data exhibited a maximum at 450 mu and minima at 400 and 500 m//, closely resembling the absorption spectrum of the P-450 CO complex [Voigt (62)]. It thus appears that the 6j3-hydroxylase system, like several other steroid hydroxylases, requires the participation of microsomal electron transport with P-450 as the terminal oxidase. 

Rat liver mlcrosomes have the capacity to convert stearoyl CoA to oleyl CoA by an enzymatic reaction requiring both oxygen and the Integrity of the NADH-llnked microsomal electron transport chain of which A9 desaturase Is the terminal component (Wilson et al., 1967). 

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