When uncoupling proteins are active, mitochondria produce heat instead of ATP. This may be useful under certain circumstances, such as when an animal is hibernating. But non-hibernating animals also have them. Particularly poorly understood is the uncoupling protein UCP2. Elena Pohl and colleagues at the University of Veterinary Medicine, Vienna, show that the protein occurs mainly in cells of the immune system. The group's highly provocative findings are published in the online journal PLOS ONE.
Mitochondria represent the powerhouses of the eukaryotic cell. They are able to use the primary product of the breakdown of sugars to generate a proton gradient across their inner membrane and to exploit this gradient to produce ATP, which drives cellular metabolism. The importance of mitochondria to higher life forms is clear from what happens when their function is blocked: many poisons, such as cyanide, are known to act in this manner.
In this light, the discovery in 1973 of a eukaryotic protein that dissipates the proton gradient without generating ATP was highly unexpected. When this protein, thermogenin, is active, mitochondria produce heat rather than ATP. We now know that thermogenin is merely one member of a family of so-called 'uncoupling proteins' that can use proton gradients to generate heat. The founder member of the family, thermogenin, has been renamed uncoupling protein 1 or UCP1 and is known to be important in helping animals keep warm during hibernation and for babies to maintain their body temperature. The actions of the other members of the family are less well understood. Particularly enigmatic is UCP2 but important clues to its function have now been provided by Anne Rupprecht and colleagues in the Institute of Physiology at the University of Veterinary Medicine, Vienna. Together with collaboration partners in Germany and Sweden, the researchers carefully examined the distribution of the UCP2 protein in mice.
|Contact: Elena Pohl|
University of Veterinary Medicine -- Vienna