Mitosome

Mitosomen are organelles that occur in some unicellular, anaerobic or microaerophilic eukaryotic organisms. This is almost certainly to greatly degenerated mitochondria, which have lost the capacity for oxidative phosphorylation. Since they were discovered only recently, they have not been particularly well studied.

General

Mitosomen occur only in unicellular eukaryotes that have no mitochondria. They were first found in Entamoeba histolytica, the cause of amoebic dysentery. Later, they were then also, for example, microsporidia Encephalitozoon cuniculi found in such and Trachipleistophora hominis. At the beginning they were also known as Crypton, this name has, however, not enforced.

Construction

Mitosomen possess just like a double mitochondrial membrane. In contrast to the mitochondrial membrane, however, no difference in potential between the intermembrane space and matrix could be determined. In spite Mitosomen in situ nick translation and antibody staining, no DNA could be detected. For older reports have been revised, the reported DNA-containing Mitosomen. Further proteins could be detected, which are related to the translocase of the inner mitochondrial membrane and the Presequence protease. In Trachipleistophora 7-47 Mitosomen were found by immunogold labeling and electron per cell that have only one -tenth the size of mitochondria with a size of about 50X90nm.

Function

Mitosomen not have the capacity for oxidative phosphorylation, the main task of mitochondria. Organisms with Mitosomen can not win on the respiratory chain ATP from the chemical energy of their food therefore. Mitosomen therefore are so far only known eukaryotic occurring under oxygen-free or oxygen-poor conditions where the oxygen for oxidative phosphorylation missing anyway. Experiments on yeast show that Mitosomen play a role in the biosynthesis of iron-sulfur clusters: the respective proteins with the corresponding proteins from Mitosomen been replaced, still a Fe - S cluster biosynthesis took place. Moreover occupied antibody markers that the Fe - S cluster synthesis takes place in the Mitosomen. When the responsible proteins are, among other things frataxin, cysteine ​​desulfurase ISU1 and mitochondriellem Hsp70.Da Fe - S proteins play essential functions, this exerts a strong selection pressure to maintain the Mitosomen. Important Fe - S proteins in eukaryotes are amitochondriellen eg Ferredoxin, hydrogenase or pyruvate ferredoxin oxidoreductase.

Origin

Almost certainly it can be said that it is highly reduced mitochondria in Mitosomen. Point out, among other things, the fact that Mitosomen have cpn60 and Hsp70 derived responsible for the folding of the proteins and imported Mitosom of mitochondrial proteins. In addition, proteins have to be imported into Mitosomen a signal sequence that enable them, when expressed in a suitable organism also the entrance to the mitochondrion or the hydrogenosome. The investigation of five related species of Entamoeba also shows that these proteins are descended from common ancestors, and were not acquired by lateral gene transfer from other organisms.

Others

Since possess no mitochondria microsporidia was assumed that it is they constitute basal eukaryotes split off from the rest of eukaryotes before the mitochondrial endosymbiosis. Only in the late 90s of the 20th century, this picture changed by the discovery of Mitosomen so that they are now placed in the vicinity of the fungi.

The hydrogenosome is another organelle, which was created by the reduction of mitochondria and allows fermentation under anaerobic and aerobic conditions. How Mitosomen have completely lost their DNA also hydrogenosomes. The only exception is the ciliate Nyctotherus ovalis, the one missing link is thus between mitochondrion and hydrogenosome.