Mitochondrial compartment

While our data using this technique are still preliminary, we have observed that 25 yU/ml insulin inhibits the rate of calcium efflux from renal slices (28). This effect of insulin was gradually reduced at the higher concentrations of insulin. The effects of insulin on calcium exchange appear to be localized in the mitochondrial compartment. Further work is needed to determine whether insulin affects specific enzyme systems which are known to play a role in renal calcium transport, and which cellular or subcellular compartments are involved. This would substantially increase our understanding of the regulation of urinary calcium excretion, and of ways in which excessive loss of calcium by this route might be avoided. 

It is contended that the renal slice technique measures primarily basolateral uptake of substrates or nephrotoxins, based on histological evidence of collapsed tubular lumens. This results in the inaccessibility of brush-border surfaces for reabsorptive transport (Burg and Orloff, 1969 Cohen and Kamm, 1976). This observation limits the ability of this model to accurately reflect reactions to nephrotoxins that occur as the result of brush-border accumulation of an injurious agent. Ultrastructurally, a number of alterations, particularly in the plasma membrane and mitochondrial compartments, have been shown to occur over a 2-h incubation period (Martel-Pelletier et al., 1977). This deterioration in morphology is very likely a consequence of the insufficient diffusion of oxygen, metabolic substrates, and waste products in the innermost regions of the kidney slice (Cohen and Kamm, 1976). Such factors also limit the use of slices in studying renal metabolism and transport functions. 

The central dogma of apoptosis is that all the initiating pro-apoptotic stimuli converge on the mitochondrial compartment. Thus, although apoptosis can be initiated elsewhere, the execution phase of apoptosis induced by ionizing radiation needs mitochondria. How do DNA lesions trigger mitochondria Several metabolic pathways coimect mitochondria to the nucleus. 

Henriquez FL, Richards , Roberts F, McLeod R, Roberts CW (2005) The unusual mitochondrial compartment of Cryptosporidium parvum. Trends Parasitol 21 68-74 Herrmann JM (2003) Converting bacteria to organelles evolution of mitochondrial protein sorting. Trends Microbiol 11 74-79... 

Hausmann A, Aguilar Netz DJ, Balk J, Pierik AJ, Muhlenhoff U, Lill R (2005) The eukaryotic P loop NTPase NBP35 An essential component of the cytosolic and nuclear iron-sulfur protein assembly machinery. Proc Natl Acad Sci USA 102 3266-3271 Henriquez FL, Richards , Roberts F, McLeod R, Roberts CW (2005) The unusual mitochondrial compartment of Cryptosporidium parvum. Trends Parasitol 21 68-74 Horner DS, Foster PG, Embley TM (2000) Iron hydrogenases and the evolution of anaerobic eukaryotes. Mol Biol Evol 17 1695-1709... 

Fig. 5.4. Two types of energy metabolism in cestodes. (a) Type 1 homolactate fermentation, (b) Type 2 Malate dismutation. Reaction 3 involves a carboxylation step decarboxylation occurs at 6, 7 and 10. Reducing equivalents are generated at reactions 6 and 7 one reducing equivalent is used at reaction 9. Thus, when the mitochondrial compartment is in redox balance and malate is the sole substrate, twice as much propionate as acetate is produced. Key 1, pyruvate kinase 2, lactate dehydrogenase 3, phosphoenolpyruvate carboxykinase 4, malate dehydrogenase 5, mitochondrial membrane 6 malic enzyme 7, pyruvate dehydrogenase complex 8, fumarase 9, fumarate reductase 10, succinate decarboxylase complex. indicates reactions at which ATP is synthesised from ADP cyt, cytosol mit, mitochondrion. (After Bryant Flockhart, 1986.)...

These organelles are the sites of energy production of aerobic cells and contain the enzymes of the tricarboxylic acid cycle, the respiratory chain, and the fatty acid oxidation system. The mitochondrion is bounded by a pair of specialized membranes that define the separate mitochondrial compartments, the internal matrix space and an intermembrane space. Molecules of 10,000 daltons or less can penetrate the outer membrane, but most of these molecules cannot pass the selectively permeable inner membrane. By a series of infoldings, the internal membrane forms cristae in the matrix space. The components of the respiratory chain and the enzyme complex that makes ATP are embedded in the inner membrane as well as a number of transport proteins that make it selectively permeable to small molecules that are metabolized by the enzymes in the matrix space. Matrix enzymes include those of the tricarboxylic acid cycle, the fatty acid oxidation system, and others. 

Two different superoxide dismutases (SODs) are found in mammalian tissues a Cu/Zn-containing enzyme which is found in the cytoplasm of most cells, and a further Mn-containing enzyme present within the mitochondrial compartment [1], Both enzymes catalyse the same reaction ... 

Previously, Tangeras [52] had proposed that a pool of iron in the inner mitochondrial compartment (1 nmol mg of protein) is available to ferrochelatase for heme formation. A soluble component of that compartment could maintain sufficient ferrous iron in equilibrium with ferric iron, allowing the observed rate of 0.3 nmol of heme formation per hour, which corresponds to an amount of about five times that necessary for the turnover of hemoproteins in hepatocytes [53]. 

Yes. Because CoA cannot freely cross membranes, not only do the cytoplasmic and mitochondrial compartments contain separate pools of CoA, but also the acetyl CoA-to-CoA ratio can be quite different in each compartment. Similarly, mitochondrial and cytosolic NAD and NADH pools are wholly separate and the NADH to NAD ratio on one side of the mitochondrial membrane can be different from that on the other side. 

Mitochondria play a key role in cell death by releasing pro-apoptotic proteins from the mitochondrial compartment. Understanding the mechanisms of mitochondrial release following a death signal is an active area of investigation and debate. An array of models has been proposed to describe the mitochondrial release of these factors in the literature. 

If radioactive amino acids are incorporated into mitochondrial proteins in vitro radioactivity is associated with mitoribosomes (Ashwell and Work, 1970). But this activity can be removed by puromycin treatment, suggesting that the radioactivity is the result of incomplete peptide chains on the mitoribosomes. There is no evidence that any mitochondrial ribosomal proteins are labeled in vitro although a clear-cut separation of the ribosomal proteins from animal cells has not been reported. Even with N. crassa no evidence was found that ribosomal proteins are coded for by mt DNA (Lizardi and Luck, 1972). From all these data it seems very likely that mitochondrial proteins are synthesized outside the mitochondria, under control of the nuclear genome, and are subsequently transported into the mitochondrial compartment. 

The enlargement of the mitochondrial compartment in male Wistar rats placed on a copper-deficient diet at 10 days of age (Dallman and Goodman 1970) is related to the depletion of cytochromes and in activity of cytochrome oxidase (Dallman 1967). By feeding weanling mice the copper-chelating agent, cuprizone, Tandler and Hoppel (1972) considerably enhanced the number of cardiac mitochondria and the frequency of occurrence of partitioned mitochondria. 

Folate metabolism is not limited to the cytoplasmic compartment. Most of the folate in tissues is found in the mitochondrion and cytosol (Horne et al. 1997). Individual folate-dependent pathways are compartmentalized within organelles. The cytoplasmic and mitochondrial compartments each possess a parallel array of enzymes catalysing the interconversion of folate coenzymes that carry one-carbon units. The mitochondrial folate metabolism favours incorporation of one-carbon groups from serine and release of formate, while the cytoplasmic metabolism favours incorporation of one-carbon units from formate with purine and thymidine synthesis and homocysteine remethylation. 

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