Arctic fish

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... 

Toxaphene accumulates in tissues of many aquatic species, especially in lipid-rich tissues of polar fish and marine mammals (Swackhamer and McConnell 1993). Toxaphene concentrations in livers of Arctic fishes of 2.9 mg/kg FW and in Canadian cod liver oil of 28 mg/kg FW are recorded... 

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... 

Another major difference between certain Arctic fishes and Antarctic notothenioids is the occurrence of a second family of AFPs in the former fishes skin AFPs. The discovery by Gong et al. (1996) that AFPs may exist within cells as well as in the extracellular fluids, and that the intracellular AFPs are encoded by a set of genes distinct from those encoding extra-... 

The seasonal variation in thermal hysteresis found in D. canadensis is due to more than shifts in concentrations of THPs, however. Unlike the freezing-avoidance strategy of Antarctic and Arctic fishes, in which the amount of thermal hysteresis appears to be due strictly to the concentration of THPs in the body fluids, freeze-avoiding insects employ a complex set of mechanisms to achieve the high levels of thermal hysteresis found for hemolymph in winter-collected specimens. 

Scholander and co-workers (1953, 1957 Gordon et al., 1962) made some of the initial significant observations on freezing resistances in fishes that could be interpreted on a molecular basis. They reported that the blood sera of Arctic fish had lower freezing temperatures than did the blood seras of fish not adapted to the cold. But, most important, they observed that the substances in the serum that helped to lower the freezing temperature were not due to salts, and that on chemical fractionation of the serum these substances were found in the fraction soluble in trichloroacetic acid. Other workers (Lievestad, 1965) also conducted related studies but in a more physiological vein. 

Some arctic fishes make unique antifreeze proteins that prevent ice crystals from forming in their blood. Scientists have transferred the genes for these proteins to tomato plants to make the plants tolerant of cold weather. 

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. 

ROBLES V, CABRITA E, FLETCHER GL, SHEARS MA, KESG Ml and HERRAEZ MP (2005) Vitrification assays with embryos from a cold tolerant snb-arctic fish species. Theriogenology, 64,1633-1646. 

Suppose we want to know the enthalpy of a particular reaction at body temperature, 37°C, but have data available for 25 C, or suppose we want to know whether the oxidation of glucose is more exothermic when it takes place inside an Arctic fish that inhabits water at 0 C than when it takes place at mammalian body temperatures. In precise work, every attempt would be made to measure the reaction enthalpy at the temperature of interest, but it is useful to have a rapid way of estimating the sign and even a moderately reliable numerical value. 

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