Notothenioid fishes

Figure 7.3 illustrates values of /ceat for orthologs of A4-LDH from vertebrates adapted to temperatures between — 1.86°C (Antarctic notothenioid fishes) and approximately 37 42°C (mammal, birds, and a thermophilic reptile) (Fields and Somero, 1998). All kalt values... 

Figure 7.4. Temperature compensation of LDH (upper panel) and citrate synthase (CS) (lower panel) activity in brains of Antarctic notothenioid fishes and tropical fishes. Enzymatic activity in homogenates of brain was measured at a common temperature, 10°C, and extrapolated to the approximate habitat temperatures of the species (0°C for Antarctic fish and 25°C for tropical species) using experimentally determined Q10 values. Activities at habitat temperatures are indicated in the figure. Despite substantial temperature compensation, an approximately twofold difference in activity persists at habitat temperatures for both enzymes. (Data from Kawall et al., 2001).

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. 

Somero, G.N., P.A. Fields, G.E. Hofmann, R.B. Weinstein, and H. Kawall (1998). Cold adaptation and stenothermy in Antarctic notothenioid fishes What has been gained and what has been lost In Fishes of Antarctica. A Biological Overview, pp. 97-109, ed. G. di Prisco, E. Pisano, and A. Clarke. Milan Springer. 

Chen, L., DeVries, A. L. and Cheng, C.-H. C. (1997). Convergent evolution of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod. Proceedings of the National Academy of Sciences, USA, 94, 3817-22. 

Figure 7.39. The diversity of antifreeze proteins and antifreeze glycoproteins in marine fishes. Shown are the structures of four types of AFPs (I-IV) and the AFGP found in Antarctic notothenioids and Arctic cod. AFPs I-IV are shown as ribbon structures. The tripeptide repeat (-ala-ala-thr-) and carbohydrate moiety (galactosyl-lV-acetylgalactosamine) of AFGPs illustrate the key element of AFGP structures in noto-thenioid and Arctic cod.

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-... 

Figure 7.43. Effects of glycerol concentration and temperature on activities of A4-LDH from an Antarctic notothenioid (Parachaenichthys charcoti) and a warm-temperate goby fish (Gillichthys mirabilis). Inset the effects of glycerol concentration on the two orthologs at physiological temperatures of the species, 0°C for P. charcoti and 20°C for G. mirabilis. (Modified after Fields et al., 2001.)...

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