Antifreeze glycoprotein, from fish

Feeney, R. E., Bnrcham, T. S., and Yeh, Y, 1986. Antifreeze glycoproteins from polar fish blood. Annual Review of Biophysical Chemistry 15 59-78. 

Fish living in Arctic and Antarctic waters may encounter temperatures as low as -1.9°C. The freezing point depression provided by dissolved salts and proteins in the blood is insufficient to protect the fish from freezing. As winter approaches, they synthesize and accumulate in their blood serum a series of eight or more special antifreeze proteins.a d One type of antifreeze glycoprotein from winter flounder contains the following unit repeated 17-50 times. 

From Table I it can be seen that fish serum from cold ocean waters may have freezing temperatures as low as — 1.4°C, but not as low as those containing the antifreeze glycoproteins. The fish with freezing temperatures only as low as — 1.4°C were found in the Arctic south of the iceberg latitudes. The polar cod, containing the antifreeze glyco-... 

An exotic function of glycoproteins is to act as antifreezes. Specifically, a number of Antarctic fish live in water cooled to about -1.9°C, a temperature below the freezing point of water and below that where the blood, mostly water, of these fish is expected to freeze. Clearly, this would be a disaster for these fish. They are saved from this fate by antifreeze glycoproteins. These proteins contain about 50 repeats of the tripeptide Ala-Ala-Thr. To each of these threonine residues is hooked a specific disaccharide. 

Chen, L., A.L. DeVries, and C.-H. C. Cheng (1997a). Evolution of antifreeze glycoprotein gene from a trypsinogen gene in Antarctic notothenioid fish. Proc. Natl. Acad. Sci. USA 94 3811-3816. 

Antarctic fishes live in -1.9°C waters, well below the temperature at which their blood is expected to freeze. These fishes are prevented from freezing by antifreeze glycoproteins present in their body. 

III. Preparation and Properties of Antifreeze Glycoprotein (AFGP) from Antarctic Fish Bloods. 198... 

The existence of an antifreeze-like substance in northern polar fish has been confirmed more recently by Scholander and Maggert (15), Hargens (16), and Raymond et al. (17), who found it in the saffron cod, Eleginus gracilis. An antifreeze substance also has been reported in the winter flounder (Pseudopleuronectes americanus) (18,19,20). Our laboratory recently has found antifreeze glycoproteins in the polar cod (Boreogadus saida) from the Barents Sea north of Russia (10). 

The glycosyltransferases used in these studies were all well characterised and were apparently pure in that each was an homogeneous enzyme protein. They are listed, with their sources, in Table 4.1. Artificial substrates for these enzymes were prepared from human transferrin and its asialo-derivative, and from the antifreeze glycoprotein of the serum of the arctic fish Dissostichus mawsoni. The structures of these substrates are given in Table 4.2. 

As to other organic substances in this context, special mention must be made of glycoproteins, which prevent blood from freezing in Arctic and Antarctic fish (De Vries, 1970 Hochachka and Somero, 1973). Glycoprotein, composed of repeated subunits of alanine and threonine bound to a disaccharide derivative of galactose, is an antifreeze agent (DeVries, 1971 Shier et al., 1972). It impedes crystal formation in blood and lowers the freezing point to -1.8°C, the lowest... 

In most proteins the proportion of each of the different a.a. residues, calculated as a percent of the total number of residues, ranges from 0 to about 30%. In extreme cases it may even reach 50%. Cereal proteins are generally very poor in Lys. Several major grains are deficient in Thr, Leu, Met, Val, and Trp. In most collagens there are no Cys and Trp residues, while the content of Gly, Pro, and Ala is 328, 118, and 104 residues/1000 residues, respectively. Paramyosin, abundant in the muscles of marine invertebrates, is rich in Glu (20-24%), Asp (12%), Arg (12%), and Lys (9%). The antifreeze fish serum glycoproteins contain several a.a. sequences of Thr-X2-Y-X7, where X is predominantly Ala and Y a polar residue. The antifreeze proteins of type I usually contain more than 60 mol% of Ala. Thr and Y, and in various antifreeze... 

---