Fish glycoproteins

Franks, F., Darlington, J., Schenz, T., Mathias, S.F., Slade, L. LeVine, H. (1987). Antifreeze activity of antarctic fish glycoprotein and a synthetic polymer. Nature 325, 146-7. 

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

A unique family of O-linked glycoproteins permits fish to live in the icy seawater of the Arctic and Antarctic regions where water temperature may reach as low as — 1.9°C. Antifreeze glycoproteins (AFGPs) are found in the blood of nearly all Antarctic fish and at least five Arctic fish. These glycoproteins have the peptide structure... 

Interacts with polar sites of glycoproteins in epidermal mucus of fish... 

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. 

Vitamin B12 (cyanocobalamin) is produced by bacteria B12 generated in the colon, however, is unavailable for absorption (see below). liver, meat, fish, and milk products are rich sources of the vitamin. The minimal requirement is about 1 pg/d. Enteral absorption of vitamin B 2 requires so-called intrinsic factor from parietal cells of the stomach. The complex formed with this glycoprotein undergoes endocytosis in the ileum. Bound to its transport protein, transcobalamin, vitamin B12 is destined for storage in the liver or uptake into tissues. 

Glycoproteins are needed as lubricants, and also function as protective agents of surfaces. The viscosity of mucins is due to the carbohydrate moiety.393 Some species of arctic fish contain an antifreeze glycoprotein that lowers the freezing point of their blood408 by preventing the lattice fonnation of water-ice clusters, a step that is a prerequisite... 

C. Sato, K. Kitajima, I. Tazawa, Y. Inoue, S. Inoue, and F. A. Troy, Structural diversity in the a-2—>8-linked polysialic acid chains in salmonid fish egg glycoproteins, J. Biol. Chem. 268 23675 (1993). 

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. 

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... 

De Vries, A.L. (1971). Glycoproteins as biological antifreeze agents in Antarctic fishes. Science, New York 172,1152-1155. 

Kychanov, V.M. (1981). On the serum proteins, lipo- and glycoproteins of white fish in the process of gonad maturation (In Russian). Voprosy Ikhtiologii 21, 489-497. 

Shier, W.T., Lin, Y. and De Vries, A.L. (1972). Structure and mode of action of glycoproteins from an Antarctic fish. Biochimica et BiophysicaActa 263,406-413. 

The Absence of Carbohydrate Specific Hepatic Receptors for Serum Glycoproteins in Fish... 

In view of the presumed role of these unique proteins in the regulation of serum glycoprotein homeostasis, it became of interest to determine whether fish, a more primitive evolutionary species, exhibited a similar or divergent control mechanism. 

The rapid, carbohydrate dependent clearance of specifically modified serum glycoproteins, observed in mammalian species (1), was not demonstrable in fish. Of the five proteins examined in Fig. 1, no significantly increased rate of disappearance from the circulation could be correlated with the nature of the terminal, non-reducing glycoside moiety. The marginally faster clearance observed in the case of asialo-orosomucoid, although reproducible, could not be ascribed to the participation of a specific hepatic receptor. This conclusion is supported by the data in Table 1 whereby it is evident that there was no selective accumulation of radioactivity in the liver the major portion of counts recoverable 25 minutes after inj ection were located in the kidneys. 

From the above evidence, it seems reasonable to infer that the hepatic receptors for galactose- and N-acetylglucosamine-terminated serum proteins present in mammals and birds, respectively, emerged at an evolutionary stage later than that of fish. The nature of the control mechanisms regulating the metabolism of serum glycoproteins in fish remains obscure. 

The molecular mechanism whereby cells recognize, interact with, and internalize glycoprotein molecules is discussed in two papers. Distler and colleagues describe the much studied but controversial role of glycosidically bound D-mannose-6-phosphate in the cellular assimilation of the enzyme /J-D-galactosidase Ashwell and Morgan study the metabolic fate of plasma glycoproteins in fish. 

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