Respiratory chain elements

Not all the cellular DNA is in the nucleus some is found in the mitochondria. In addition, mitochondria contain RNA as well as several enzymes used for protein synthesis. Interestingly, mitochond-rial RNA and DNA bear a closer resemblance to the nucleic acid of bacterial cells than they do to animal cells. For example, the rather small DNA molecule of the mitochondrion is circular and does not form nucleosomes. Its information is contained in approximately 16,500 nucleotides that func-tion in the synthesis of two ribosomal and 22 transfer RNAs (tRNAs). In addition, mitochondrial DNA codes for the synthesis of 13 proteins, all components of the respiratory chain and the oxidative phosphorylation system. Still, mitochondrial DNA does not contain sufficient information for the synthesis of all mitochondrial proteins most are coded by nuclear genes. Most mitochondrial proteins are synthesized in the cytosol from nuclear-derived messenger RNAs (mRNAs) and then transported into the mito-chondria, where they contribute to both the structural and the functional elements of this organelle. Because mitochondria are inherited cytoplasmically, an individual does not necessarily receive mitochondrial nucleic acid equally from each parent. In fact, mito-chondria are inherited maternally. 

Iron (Fe) is quantitatively the most important trace element (see p. 362). The human body contains 4-5 g iron, which is almost exclusively present in protein-bound form. Approximately three-quarters of the total amount is found in heme proteins (see pp. 106,192), mainly hemoglobin and myoglobin. About 1% of the iron is bound in iron-sulfur clusters (see p. 106), which function as cofactors in the respiratory chain, in photosynthesis, and in other redox chains. The remainder consists of iron in transport and storage proteins (transferrin, ferritin see B). 

Strobilurin A, Strobilurin and Myxothiazole new inhibitors of the bci segment of the respiratory chain with an ( )-/l-methoxyacrylate system as common structural elements , FEBS Lett., 1981,132, 329-333. 

However, the details of the molecular mechanism of redox-linked proton translocation are still largely unknown, not only for cytochrome oxidase but for the entire respiratory chain. In considering various possibilities it is important to distinguish between basically different elementary steps of the process. Proton conduction through the protein is but one such element. Several possible mechanisms have been proposed for this function, based on conduction along hydrogen-bonded networks of amino acid residues within the membrane (reviewed in Ref. 8). In redox-linked... 

In Section II the composition and organisation of the respiratory chains of P. versutus and P. denitrificans will be reviewed. The gene organization and composition, and their possible control elements, will also be discussed. Section III will deal with the structure and function of the four components of the MADH redox chain. Structures determined by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) techniques are available for the members of the MADH chain or for closely related analogues. Finally, the enz3unology and reaction kinetics of the chain will be reviewed. 

The criteria usually used to demonstrate the participation of a biochemical component in the electron transport chain have been admirably satisfied for cytochrome c. Therefore, this compound undoubtedly is an important element of the electron transport chain. A variety of quantitative methods demonstrate that the amount of enzyme in the system is consistently proportionate to the amounts of the other elements of the electron transport chain. If the enzyme is removed from the respiring particles, electron transport is blocked. It can be restored by adding pure cytochrome c. Moreover, the rate of reduction of cytochrome c in heart mitochondria is in keeping with its role in the main respiratory chain. 

The main function of sodium and potassium in the body, with chloride as the counter ion, is to maintain the osmotic pressure of fluids outside and inside cells and acid-base equilibrium. In addition, these elements are required for the activation of some enzymes, such as sodium for activatation of a-amylase and potassium for activation of glycolytic enzymes and respiratory chain enzymes. Potassium significantly affects muscle activity, especially the activity of cardiac muscle. 

This group of proteins is ubiquitous. Most of the iron-sulfur proteins transfer electrons at negative redox potentials, e.g. in the respiratory chain or in photosynthesis, but some possess enzymatic, sensing or regulatory activity and they can also be involved in stabilization of protein domain structures or in radical formation. The important role of the element combination iron and sulfur in biology derives from many factors including availability, solubility and reactivity. The role of the sulfur ligands has been reviewed recently. For more reviews of various EPR-related aspects the reader is referred to the earlier report in this series. 

The inner membrane of the mitochondrion accounts for 80-95% of the protein found in mitochondrial membranes and over 90% of the lipid. It is the site of the respiratory chain and the synthesis of ATP. It is this membrane, in conjunction with studies on transport through the plasma membrane, that has contributed most forcefully both to the viewpoint of the anisotropic organization of membrane structural elements and of biochemical events carried out by or in membranes. As regards mitochondria, the interaction of the inner membrane components in carrying out electron transport and oxidative phosphorylation is the focal investigative question both for mitochondrial function and for the organization of vectorial events in general. 

Zhou et al. [175] described the determination of severe acute respiratory syndrome (SARS) coronavirus by a microfluidic chip system. The unit included an LIF microfluidic chip analyzer, a glass microchip for both PCR and capillary electrophoresis, a chip thermal cycler based on dual Peltier thermoelectric elements, a reverse transcription-polymerase chain reaction (RT-PCR) SARS diagnostic kit, and a DNA electrophoretic sizing kit. According to the authors, the system allowed efficient DNA amplification of the SARS coronavirus followed by electrophoretic sizing and detection on the same chip. 

Copper and Zinc in Aerobic Metabolism. Cytochrome oxidase, the terminal oxidase in the electron transport chain contains an atom of copper. On this enzyme the protons and electrons generated during oxidative metabolism combine with elemental oxygen to form water. During copper deficiency the tissue concentration of cytochrome oxidase is reduced. While the effects of lower cytochrome oxidase activity on exercise has not been described, it is likely that aerobic energy metabolism will be diminished. This effect of copper deficiency was first described in animals with myelin aplasls — the degeneration myelin (86). The oxidative process of phospholipid synthesis, a primary component of myelin, was depressed. Liver mitochondria had impaired respiratory activity (87). Cytochrome oxidase activity was also depressed in brain, heart and liver. 

The dioxygen reduction site of the key respiratory enzyme, cytochrome c oxidase [E.C. 1.9.3.1], is a bimetallic catalytic center comprised of a heme iron adjacent to a Type 2 mononuclear copper center (see Cytochrome Oxidase). The recent solution of the X-ray crystal structure of this enzyme revealed an entirely unanticipated covalent modification of the protein structure, a cross-link between a histidine and tyrosine side chain (23) within the active site (Figure 2)." This extraordinary posttranslational modification has been confirmed by peptide mapping and mass spectrometry, and has been detected as a conserved element in cytochrome c oxidases isolated from organisms ranging from bacteria to cows. The role of the cross-linked structure in the function of cytochrome c oxidase is still controversial." " ... 

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