System mitochondrial

Numerous experiments were then performed with mitochondria incubated with acetate, CoA, ATP, etc., in attempts to detect fatty acid synthesis. In 1957, Lynen and his colleagues reported the presence in mitochondria of a system which catalyzed the elongation of caproyl CoA to octanoyl CoA by the addition of an acetate unit. NADH and NADPH had to be present. The existence of this mitochondrial system was confirmed by Wakil et al. in 1961 who showed the 12C acid could be extended to 16C by successive additions of 2C fragments. 

Mitochondrial system The function of the mitochondrial cyto chrome P450 monooxygenase system is to participate in the hydroxylation of steroids, a process that makes these hydropho bic compounds more water soluble. For example, in the steroid hormone-producing tissues, such as the placenta, ovaries, testes, and adrenal cortex, it is used to hydroxylate intermediates in the conversion of cholesterol to steroid hormones. The liver uses this system in bile acid synthesis (see p. 222), and the kidney uses it to hydroxylate vitamin 25-hydroxycholecalciferol (vitamin D, see p. 384) to its biologically active 1,25-hydroxylated form. 

Lehninger, A.L., 1974, Role of phosphate and other proton-donating anions in respiration-coupled transport of Ca2+ by mitochondria, Proc. Natl. Acad. Sci. USA 71, pp. 1520-1524 Lehninger, A.L., Carafoli, E., and Rossi, C. S., 1967, Energy-linked ion movements in mitochondrial systems, Adv. Enzymol. Relat. Areas. Mol. Biol. 29, pp. 259-320 Lemasters, J.J., Nieminen, A. L., Qian, T., Trost, L., Elmore, S. P., Nishimura, Y., Crowe, R. A., Cascio, W. E., Bradham, C. A., Brenner, D. A., and Herman, B., 1998, The mitochondrial permeability transition in cell death A common mechanism in necrosis, apoptosis and autophagy, Biochim. Biophys. Acta 1366, pp. 177-196... 

Fig. 8.2 Glycolysis and related pathways. Glycolysis is a central metabolic machinery in which one mole of glucose is catabolized to two moles of pyruvate, NADH, and ATP. Under aerobic conditions, pyruvate is further oxidized by mitochondrial system. In erythrocytes DHAP is a dead-end product however, in brain it can be converted into direction of lipid synthesis. Glycolysis and the pentose phosphate pathway (pentosePP) are interconnected via fructose-6-P and glyceral-dehyde-3-P. A high level of NADPH favors lipid synthesis via pentose phosphate shunt (pentosePP). At TPI inhibition (TPI deficiency), glyceraldehyde-3-Pcan be produced via G6PDH as well, to contribute to the glycolytic flux. a-GDH catalyzes the...

The development of toxic symptoms on plants treated with pure electron transport inhibitors, such as simazine, diuron, and the uracils, can be prevented if the plants are supplied exogenously with a respirable carbohydrate (2). This observation suggests that the glycolytic or the mitochondrial system can provide sufficient energy to prevent the appearance of phyto-... 

This inequality means that a maximal net rate of ATP production is incompatible with the optimal efficiency. Cellular pathways balance the rate and efficiency of ATP production with respect to the energy needs of the cell. For example, heart and brain mitochondrial systems utilize more oxygen and produce ATP at a faster rate than the... 

Kun, E., Kirsten, E., Sharma, M.L. (1977). Enzymatic formation of glutathione-citryl thioester by a mitochondrial system and its inhibition by (-)erythrofluorocitrate (glutathione-S-citryl ester/metalloprotein/inner mitochondrial membrane/fluoroci-trate toxic mechanism). Proc. Natl Acad. Sci. USA 74 4942-6. 

No -pumping activity has yet been described for either preparation and this aspect of the coupling between electron transport and PP synthesis in the mitochondrial system is thus still an unsolved question. 

The conclusion that mitochondria may be essentially inactive in the intracellular Ca " homeostasis during normal conditions, and only become activated when emergency situations must be controlled (or, possibly, in response to pharmacological influences), may sound excessively negative. Conceptually, it would seem difficult to justify the development of such a sophisticated machinery as that for the transport of Ca " in and out of mitochondria if its use would only be limited to the improbable cases where cytosolic Ca is allowed to fluctuate widely out of the normal limits. It may well be, however, that the primary reason for the development of the systems that constitute the Ca cycle of mitochondria has not been the control of cytosolic Ca under normal physiological conditions. The kinetic limitations of the mitochondrial system, and the existence in cells of other membrane structures capable of transporting Ca back and forth more efficiently than mitochondria under normal in situ conditions, are undisputable facts. Even the role... 

The mitochondrial system uses acetyl-CoA, not malonyl-CoA, by a slightly modified reversal of j6-oxidation. The substrates are saturated and unsaturated Ci2, Ci4, and Ci6 fatty acids, and the products are Cig, C20, C22, and C24 fatty acids. The first reduction step utilizes NADH, and the enzyme is /5-hydroxyacyl dehydrogenase (a -oxidation enzyme) the second reduction step utilizes NADPH, and the enzyme is enoyl reductase. 

Recent studies have indicated that in addition to mitochondria, peroxisomes are capable of removing acetyl-CoA moieties from long-chain fatty acids. The peroxisomal P-oxidative pathway is different in two major respects from the mitochondrial system. First, the hydrogen atoms removed are oxidized to water via H2O2. This process does not generate energy in the form of ATP. Second, peroxisomal P-oxidation stops when octanoyl-CoA (C8-C0A) is produced. 

An even more sensitive system for Ca uptake from cytoplasm exists in microsomal preparations that are enriched in endoplasmic reticulum. The for Ca + uptake in microsomes has been reported to be approximately 1 p,M, which makes the uptake system 20 to 40 times more sensitive than the mitochondrial systems. Initial studies indicate that the endoplasmic reticular uptake systems require the hydrolysis of ATP. To date, these transport systems have not been purified and little is known about their physiological role in Ca " " regulation. 

That the mitochondrial system almost exclusively hydroxylates the 25-pro-5 methyl group was later confirmed in vitro with 5)8-cholestane-3a,7a,12a-triol and 5/8-cholestane-3 ,7a-diol as substrates [123,124]. Gustafsson and Sjostedt showed that the microsomal fraction of rat liver mainly hydroxylates the 25-pro-/ methyl group of 5)S-cholestane-3a,7 ,12a-triol [125]. 

It is evident that the microsomal and mitochondrial systems have opposite specificities. Since Popjak et al. have suggested that the 25-pro-/ methyl group should be denoted C-26 and the 25-pro-S methyl group C-27 [119], the mitochondrial w-hydroxylation may be regarded as a 27- and the microsomal as a 26-hydroxyl-ation. In this review, hydroxylation of any of the two methyl groups will be referred to as a 26-hydroxylation. 

It is important for the cell to convert the potential energy in reduced coenzymes formed in glycolysis, and particularly the citric-acid cycle, into utilizable energy in the form of ATP. This is accomplished by a mitochondrial system that is part of the inner membrane and is referred to as the electron-transport system (Fig. 

The mitochondrial system, with its two unidirectional modes, avoids the need to simultaneously synthesize leading and lagging strands. As a result, both strands are made in a continuous fashion-no Okazaki fragments. 

In animal experiments with chronic ingestion of small amounts of thallium, damage and changes in the mitochondrial system of nervous cells have also been observed. Humans exposed chronically to small amounts of thallium revealed not the typical symptoms of thallium toxicity, the most consistent findings being polyneuropathy and psychiatric changes (Kazantzis 1986). 

In all of the hgures mentioned, down corresponds to inside the membrane, and up is outside. In other words, in Rhodopseudomonas viridis the special pair of chlorophylls is near the cytoplasmic side of the membrane (inside the cell), whereas in both photosystems I and II, the special pairs are near the stroma and away from the thy-lakoid lumen, that is, facing outward. This is interesting because other structures in the thylakoid membrane are also upside down compared to bacterial and mitochondrial systems. 

Another enzymatic oxidation of proline has recently been described by Boggess et al. (1978). They found isolated mitochondria from several higher plants (barley, com, wheat, soy, and mung bean) could oxidize proline to glutamate, organic acids, and CO2. Pyrroline-5-carboxylate was apparently the primary product of this reaction. The reaction required O2 and could not be carried out anaerobically with a pyridine nucleotide acceptor. The for L-proline with the mitochondrial system was 5 mAf. Boggess et al. (1978) were not able to solubilize this system. Treatment with Triton X-100 yielded inactive preparations. 

Having CATa and CATb on either side of the microsomal membrane appears to serve no obvious purpose unless, by analogy with the well-characterized mitochondrial system,these are linked to some form of transport system to move fatty acylcamitines across the membrane. It is impractical to study directly the transport of radiolabelled long-chain fatty acylcamitines into or out of sealed microsomal vesicles because these metabolites bind non-specifically to many cellular proteins. We, therefore, devised a way to do this indirectly, based on the use of the lumenal enzyme ethanol acyltransferase (EAT) as a reporter . In the endoplasmic reticulum EAT ° catalyzes the reaction ... 

DNA, proteins, lipids, etc.) occurs [29]. It leads to neuronal damage especially of mitochondrial system. 

C. Mitochondrial System for the Oxidation of Saturated Fatty Acids 360... 

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