Proteins in mitochondria

A decade after the discovery of the Rieske protein in mitochondria (90), a similar FeS protein was identified in spinach chloroplasts (91) on the basis of its unique EPR spectrum and its unusually high reduction potential. In 1981, the Rieske protein was shown to be present in purified cytochrome Sg/complex from spinach (92) and cyanobacteria (93). In addition to the discovery in oxygenic photosynthesis, Rieske centers have been detected in both single-RC photosynthetic systems [2] (e.g., R. sphaeroides (94), Chloroflexus (95)) and [1] (Chlo-robium limicola (96, 97), H. chlorum (98)). They form the subject of a review in this volume. 

Iron-Sulfur Proteins in Mitochondria and Other Cell Compartments... 

Miyagishima SY, Nozaki H, Nishida K, Matsuzaki M, Kuroiwa T (2004) Two types of FtsZ proteins in mitochondria and red-lineage chloroplasts the duplication of FtsZ is implicated in endosymbiosis. J Mol Evol 58 291-303... 

Biosyntheses of DNA, RNA and proteins in mitochondria can be another example of constructive metabolic function of these organelles. It certainly requires ATP and therefore is alternative to energy supply for extramitochondrial ATP-consuming processes [5]. 

Mitochondria can replicate by division however, most of their proteins must be imported from the cytosol. Mitochondria contain a small amount of DNA, which encodes for only 13 different subunits of proteins involved in oxidative phosphorylation. Most of the enzymes and proteins in mitochondria are encoded by nuclear DNA and synthesized on cytoplasmic ribosomes. They are imported... 

Most of the proteins in mitochondria are encoded in the nuclear genome. These include all the enzymes required to synthesize the DNA in the mitochondrial chromosome, the enzymes of the citric acid cycle, and many of the soluble enzymes in oxidative phosphorylation. 

In the electron transfer cytochromes the iron of heme is bound in a hexacoordinate low-spin state, with two protein ligands (typically histidine and/or methionine) above and below the heme plane. They serve as electron carrier proteins in mitochondria and endoplasmatic organelles as well as in bacterial redox chains. At least three classes of cytochromes, a, b and c, are known. They can alternate between an oxidized Fe(III) low-spin state with a single unpaired eleetron and a reduced Fe(II) low-spin form with no unpaired electrons. Since iron remains low spin, electron transfer is greatly facilitated. The best characterized family are the c cytochromes. 

The enzymatic transfer of ADPR to an acceptor protein in mitochondria was reported in rat liver and in testis (for review see [24, 25]). Recently, Hilz described a non-enzymic ADP-ribosylation of specific mitochondrial acceptors [26]. 

The second major system is the mammalian Lon protease. Lon is primarily localized in mitochondria, with some data indicating that a Lon variant is transported to peroxisomes. Localization to an organelle such as the mitochondria is cruciaL since the mitochondrial structure is enclosed by a double membrane system, making it impermeable to proteasome which is found throughout the rest of the cell. Mitochondria are a major source of free radical generation, and their macromolecules are highly susceptible to oxidative modification. The Lon protease is the only known system for the direct removal of oxidized proteins in mitochondria. 

Meanwhile the protein in proteolipid was shown to consist of subunits whose molecular weight ranged from 10,000 to 30,000 (E. B. Thompson and Kies, 1965). The unit of structural protein in mitochondria was estimated to have a molecular weight of 64,000 (Lenaz et al., 1968). 

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