International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Impact Factor (2012): 3.358 Volume 3 Issue 8, August 2014 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Role of Antifreezing Proteins in Fishes Vikash Kumar 1 , Suvra Roy 2 , Debtanu Barman 3 1, 2 Central Inland Fisheries Research Institute (CIFRI), Barrackpore- 700120 India 3 Center for Aquaculture Research & Development (CARD), St. Xavier’s Vocational Training Center, Don Bosco, Bishramganj, Tripura, 799103 India Abstract: Antifreeze proteins (AFP) and antifreeze glycoproteins (AFGP) comprise a structurally diverse class of proteins that have in common the ability to bind to ice and inhibit its growth. This action at the surface of ice in contact with a solution of AFP leads to a lowering of the freezing point (non-equilibrium) below the melting point, referred to as thermal hysteresis (in °C). AFPs are incorporated within ice when it freezes because of their affinity for its surface. There, even in the frozen state, they inhibit the growth of large ice crystals at the expense of small ones (recrystallization inhibition), particularly when ice approaches the melt temperature and becomes more fluid. As a result of these beneficial properties, AFPs and AFGPs have been incorporated into the freeze-resistance or freeze-tolerance strategies of many organisms such as marine fishes, insects, plants and bacteria. Keywords: Antifreeze proteins, antifreeze glycoproteins, freezing point 1. Introduction Birds, fishes, amphibians, insects and plants have evolved several strategies to cope with extreme low temperature in their natural habitat. Mechanisms involved in their cold tolerance provide valuable clues to the studies on bacterial cold tolerance. One of the major strategies adopted by the cold-tolerant fishes, insects and plants is the production of specific proteins, which help them to maintain their body fluid in the liquid state at sub-zero temperatures. In general, they are called antifreeze proteins (AFPs), though other terms such as antifreeze glycoproteins, antifreeze polypeptides are also used to denote the structural features of these antifreeze proteins.AFPs protect the organisms (Fig 1) from freezing at temperature below 1°C by binding with ice crystals and modify their growth through an adsorption- inhibition mechanism [1]. Marine teleosts living in polar waters have a body temperature of about ±1.9 0 C, the same as the ambient temperature of the surrounding seawater. However, their body fluids are hypoosmotic to sea water and have a melting point of approximately ±0.7 0 C. Thus, the polar teleosts are super-cooled by more than 1 0 C[2]-[3].One could therefore predict that the fish sooner or later would experience a lethal freezing. Polar fish are protected against freezing by thepresence in their body fluids of antifreeze proteins,which display a capacity to inhibit ice growth when partly frozen fluid samples are cooled. Figure 1: The antifreeze molecules allow ice fish to live in subfreezing water by plugging gaps in existing small ice crystals and preventing the attachment of more ice molecules. Ice crystal growth is thus effectively stopped [4]. Paper ID: 02015179 1215