Antifreeze protein
Anti -freeze proteins ( AFP ) or Eisstrukturierende proteins ( ISP) are a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria to survive in an environment with temperatures below the freezing point of water.
Anti -freeze proteins bind to ice crystals and prevent their growth and recrystallization, which would lead to death of the animal. The proteins can also interact with cell membranes of mammals, to protect them from frost damage.
Operation
Unlike the conventional antifreeze anti -freeze proteins do not lower the freezing point is proportional to its concentration, but counteract the colligative property. This allows them to be effective at concentrations that are more than 300 to 500 times lower than that of ordinary substances dissolved in the antifreeze. These concentrations have no influence on the osmotic pressure. The unusual properties of the antifreeze proteins are due to the binding property to the surface of ice crystals.
Classification
Organisms that contain anti -freeze proteins may be divided into
- Types frost avoided
- Frost - tolerant species
Frostvermeidende types
The frostvermeidende species are able to completely protect their body fluids from freezing. Typically, however, the antifreeze is canceled at extremely low temperatures, leading to a rapid growth of ice crystals and subsequent death of the animal.
Frost - tolerant species
The frost - tolerant species are able to survive the freezing of body fluids. Some of these species are thus brought to the anti -freeze proteins in context, which are effective as cryoprotectant and reduce the harmful effects of frost, but not completely cancel. The exact mechanism of action is still unknown. However, the presence of antifreeze proteins can prevent recrystallization stabilize the cell membranes, thus minimizing frost damage.
Development
The remarkable diversification and distribution of anti -freeze proteins suggests that the different types have emerged in recent years and in response to the freezing of the seas around one to two million years in the Northern Hemisphere and millions to ten to thirty years in the Antarctica. The different development of similar processes of adaptation is called " convergent evolution ". Two reasons are responsible for the fact that many types of anti -freeze proteins can perform the same function, although they are constructed differently:
History
In the 1950s, the Canadian researchers examined Scholander why Arctic fish can survive in water temperatures which lie below the freezing point of her own blood. His experiments led him to believe that there must be an antifreeze in their blood. In the late 1960s, the zoologist Arthur DeVries was able to isolate the antifreeze protein by the study of Arctic fish. At that time they were called " glycoproteins as biological antifreeze agents " and hereinafter referred to as antifreeze glycoproteins in order to distinguish it from the newly discovered biological anti -freeze proteins that were not glycoproteins. DeVries and Robert Feeney could then characterize the chemical and physical properties of anti -freeze proteins.
Published in 1992 a work at Griffith anti -freeze proteins in leaves of winter wheat. Around the same time documented Urrutia, Duman and Knight the thermal hysteresis protein (thermal hysteresis ) in angiosperms. 1993, the occurrence of anti-freeze proteins has also been found in fungi and bacteria.
Discussion on the name
More recently, attempts have been made, anti -freeze proteins to give the new name " Eisstrukturierende proteins " in order to better highlight of antifreeze and their negative image (eg, ethylene glycol ). The two things are completely different kinds of material and have only a very remote resemblance in their effect.