Inner mitochondrial membrane origins

Oxidative phosphorylation is ATP synthesis linked to the oxidation of NADH and FADH2 by electron transport through the respiratory chain. This occurs via a mechanism originally proposed as the chemiosmotic hypothesis. Energy liberated by electron transport is used to pump H+ ions out of the mitochondrion to create an electrochemical proton (H+) gradient. The protons flow back into the mitochondrion through the ATP synthase located in the inner mitochondrial membrane, and this drives ATP synthesis. Approximately three ATP molecules are synthesized per NADH oxidized and approximately two ATPs are synthesized per FADH2 oxidized. 

Many authorities believe that mitochondria have prokaryotic origins because the inner mitochondrial membrane lacks cholesterol and contains cardio-lipin. Moreover, mitochondrial DNA is circular and the ribosomes approximate the size of those from prokaryotic organisms. 

Acetyl-CoA is oxidized to C02 by the Krebs cycle, also called the tricarboxylic acid cycle or citric acid cycle. The origin of the acetyl-CoA may be pyruvate, fatty acids, amino acids, or the ketone bodies. The Krebs cycle may be considered the terminal oxidative pathway for all foodstuffs. It operates in the mitochondria, its enzymes being located in their matrices. Succinate dehydrogenase is located on the inner mitochondrial membrane and is part of the oxidative phosphorylation enzyme system as well (Chapter 17). The chemical reactions involved are summarized in Figure 18.7. The overall reaction from pyruvate can be represented by Equation (18.5) ... 

A molecular assembly in the inner mitochondrial membrane carries out the synthesis of ATP. This enzyme complex was originally called the mitochon-drial A TPase or F ATPase because it was discovered through its catalysis of the... 

Transfer of protons and electrons between complexes I and III is mediated by the hydrophobic hydrogen carrier ubiquinone. This compound, which is free to move around the inner mitochondrial membrane, is also called Coenzyme Q and Coenzyme Qiq. It carries hydrogens and is also involved in shuttling hydrogens from complex II to complex III. (It received its particular name because it is a quinonoid compound that is ubiquitous throughout the inner mitochondrial membrane. It has 10 linked isoprenoid units, and since it was originally thought to be a coenzyme, it became known as coenzyme Qiq.)... 

Dissociation of enzyme and membrane synthesis during regeneration has also been reported for the mitochondria of the rat adrenal cortex (Yago et al, 1972). After adrenal enucleation, cellular proliferation occurs, and, in about 20 days, the gland has regenerated to approximately its original size. Enucleation leads to rapid multiplication of mitochondria much smaller than normal. These mitochondria increase in size by accumulation of protein and phospholipid, the latter primarily in the inner mitochondrial membrane. In addition to the usual cytochromes, the inner membranes of adrenal cortical mitochondria of beef, swine, and rats possess a special cytochrome, cytochrome P-450, usually found in the endoplasmic reticulum. Cytochrome P-450 is carbon monoxide-sensitive... 

Recent development of mitochondrial theory of aging is so-called reductive hotspot hypothesis. De Grey [465] proposed that the cells with suppressed oxidative phosphorylation survive by reducing dioxygen at the plasma membrane rather than at the mitochondrial inner membrane. Plasma membrane redox system is apparently an origin of the conversion of superoxide into hydroxyl and peroxyl radicals and LDL oxidation. Morre et al. [466] suggested that plasma membrane oxidoreductase links the accumulation of lesions in mitochondrial DNA to the formation of reactive oxygen species on the cell surface. 

Roise, D and Maduke, M. (1994) Import of a Mitochondrial Presequence into P. Denitrificans, FEBS Letters, 337, 9-13 Cavalier-Smith, T. (1987) The Simultaneous Symbiotic Origin of Mitochondria, Chloroplasts and Microbodies, Annals of the New York Academy of Science, 503, 55-71 Cavalier-Smith, T. (1992) The Number of Symbiotic Origins of Organelles, BioSystems, 28, 91-106 Hartl, F Ostermann, J., Guiard, B and Neupert, W. (1987) Successive Translocation into and out of the Mitochondrial Matrix Targeting of Proteins to the Inner Membrane Space by a Bipartite Signal Peptide, Cell, 51,1027-1037. 

For a correct interpretation of the type of mitochondrial damage it is necessary to know the original sites of enzymes in the mitochondria. One should also realize that mitochondria consist of an outer membrane, an inner membrane, the cristae, the intracristal space, and the mitochondrial matrix. When we started our work, the locations of some enzymes in liver mitochondria had been determined but no information was available concerning the locations of the above-mentioned enzymes... 

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