Mitochondrial membrane 1950 Volume

Mitochondria are bacteria-sized organelles (about 1 X 2 im in size), which are found in large numbers in almost all eukaryotic cells. Typically, there are about 2000 mitochondria per cell, representing around 25% of the cell volume. Mitochondria are enclosed by two membranes—a smooth outer membrane and a markedly folded or tubular inner mitochondrial membrane, which has a large surface and encloses the matrix space. The folds of the inner membrane are known as cristae, and tube-like protrusions are called tubules. The intermembrane space is located between the inner and the outer membranes. 

What are the molar concentrations of the electron carriers in mitochondrial membranes In one experiment, cytochrome b was found in rat liver mitochondria to the extent of 0.28 pmol/g of protein. If we take a total mitochondrion as about 22% protein, the average concentration of the cytochrome would be 0.06 mM. Since all the cytochromes are concentrated in the inner membranes, which may account for 10% or less of the volume of the mitochondrion, the concentration of cytochromes may approach 1 mM in these membranes. This is sufficient to ensure rapid reactions with substrates. 

To determine the basis for this regular variation in rate of proton leakage, several characteristics of the mitochondria were measured, including inner membrane surface area per unit of matrix volume and fatty acid composition of mitochondrial membrane phospholipids. The largest share (about 70%) of the variation in proton flux rate appears to be due to dififer-... 

Antibodies. — A new volume of Methods in Enzymology covers the preparation and use of affinity-labelled immunoglobulins. The specialized procedures required for the preparation of ferritin-antibody conjugates have been reviewed and the use of the conjugates for the localization of enzymes in mitochondrial membranes discussed. 

In general, then, the energy conversions of biology reduce to the production of ATP and the uses of ATP, that is, the production of ATP by the five protein-based machines of the inner mitochondrial membrane and the thousands of subsequent protein-based machines that do the necessary work of the cell. This constitutes yet an enormous task that will fill hundreds of volumes in the future of protein-based machines. The intention of this volume, however, is to add a simplifying feature of a common groundwork of explanation for each of the hydrophobic and elastic consilient mechanisms. For the function of protein-based machines of biology, this perspective recovers an attractive element of simplification. 

TABLE 1. SURFACE TO VOLUME RATIO VALUES FOR CHLOROPLAST THYLAKOIDS AMD MITOCHONDRIAL MEMBRANES ... 

The level of LPO was measured with a fluorescence method [8]. Lipids were extracted by the mixture of chloroform and methanol (2 1). Lipids of mitochondrial membranes (3-5 mg of protein) were extracted in the glass homogenizer for 1 min at 10°C. Thereafter, equal volume of... 

Oscillatory behavior has also been demonstrated in mitochondrial preparations and appears to be mediated by a combination of the mitochondrial membrane and ion transport processes. Such oscillations involve volume changes, ion movements, and oxidation-reduction states of the respiratory chain proteins. Experiments have demonstrated that these oscillations require the simultaneous presence of a... 

We have measured the fractional cell volumes of the various compartments in isolated wheat protoplasts and developed a mathematical model of the cell which relates the values of the potentials across cellular membranes to the distribution of permeant ions in these compartments. This information has been used to predict how, or if, the mitochondrial membrane potential changes with illumination. The results show that it 4-ncreases in value, implying a greater limitation on mitochondrial respiration in the light. Whether the increase in membrane potential is due to adenylate control remains to be clarified. These results have considerable implication on the mechanism of oxidation of NADH produced by glycine decarboxylase. 

As the ocular muscle enters the orbit, its appearance changes dramatically. Most of the muscle cytoplasm is lost, contractile proteins largely disappear, and mitochondrial abundance increases dramatically, to assume up to about two-thirds of cell volume. Another striking feature of heater organ cells is the development of an elaborate membrane wrapping around the mitochondria (figure 7.32). This extensively developed membrane system is derived from the sarcoplasmic reticular membranes. The high densities of ion pumps in the... 

Mitochondria arc membranous organelles (Fig. 1-9) of great importance in the energy metabolism of the cell they are the source of most of the ATP (Chap. 14) and the site of many metabolic reactions. Specifically, they contain the enzymes of the citric acid cycle (Chap. 12) and the electron-transport chain (Chap. 14), which includes the main oxygen-utilizing reaction of the cell. A mammalian liver cell contains about 1.000 of these organelles about 20 percent of the cytoplasmic volume is mitochondrial. 

Several observations made in whole membranes or in the isolated complexes are in line with these concepts the shifts induced by antimycin A [110,137] and myxothiazol on the absorption spectra of cytochromes b and the alterations of the ESR spectrum of the FeS protein by UHDBT or DBMIB [131]. Moreover, the oxidant-induced reduction of cytochromes b, the key observation for accepting these electron transfer schemes, has been demonstrated in all h/c, complexes isolated so far from mitochondria [134], chloroplasts [111], cyanobacteria [112] and photosynthetic bacteria [110]. In the chloroplast b /f complex this reaction has been demonstrated also in the absence of any exogenously added quinol, indicating that possibly a structurally bound quinone (quinone is always present in the isolated complexes with a stoicheiometry of about 0.5-0.7 mol/mol of cyt. c, [110,111]) is sufficient to drive the reduction of cytochromes [138]. Since a detailed treatment of the genera] mechanism, as well as of the more specific problems of the mitochondrial respiratory chain, are reported in Chapter 3 of this volume, the following discussion will deal only with the specific features of the electron transfer chains in photosynthetic membranes. 

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