Serum antifreeze glycoprotein

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-... 

Antifreeze glycoprotein is a collective name for a family of at least eight closely related glycoproteins that account for a major fraction of the protein in the blood serum of certain Antarctic fishes. The glycoproteins have been numbered according to the order of migration of... 

Fig. 1. The antifreeze glycoproteins have been numbered according to the order of their migration during electrophoresis. The diagram shows the electrophoretic pattern of mixed antifreeze glycoproteins of Trematomus borchgrevinki serum in borate buffer in acrylamide gel numbers refer to the eight different glycoproteins found in the serum. From Vandenheede (1972).

Fig. 4. Purification of antifreeze glycoproteins from Trematomus borchgrevinki serum. Sixty-six milliliters of T. borchgrevinki serum were dialyzed against 2.5 mM Tris at pH 9.6 and chromatographed on a DEAE-cellulose column (3.3 x 100 cm) equilibrated with the same buffer. The sample size was 13 ml per tube. Fraction I was eluted with the starting buffer, and fractions II and III were eluted with 50 mM Tris-HC1 at pH 9.6. Fraction IV was eluted with 0.2 M Tris-HCl at pH 9.6, and fraction V was eluted with 2 M Tris-HCl at pH 6.8. From DeVries et at. (1970), reproduced with permission.

Saliva4 Serum fraction VIC Ovomucoid" Antifreeze glycoprotein" ... 

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. 

A similar approach has been used more recently by Miyata et al (2006) to prepare tumour marker-responsive hydrogels. These polymeric networks, prepared by biomolecular imprinting, were conjugated with lectins and antibodies so that they exhibited volume changes in response to antifreeze glycoprotein (AFP), a glycoprotein which is widely used for the serum diagnosis of primary hepatoma. 

Initial studies on the polar cod blood serum have shown that its antifreeze protein is a glycoprotein with most properties similar to those from the Antarctic species T. borchgrevinki. Both active and inactive components were obtained. The active components had the same ratios of alanine to threonine (approximately 2 1) as found in the Antarctic glycoproteins and the same contents of galactosamine and galactose. No other amino acids were found. In contrast to the comparatively low antifreeze activity of the saffron cod reported by Raymond and co-workers, the AFGP from the polar cod had an antifreeze activity similar to that from the Antarctic species. 

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... 

---