Freeze resistance in rainbow smelt (Osmerus mordax) : seasonal patterns of glycerol and antifreeze protein accumulation and the in vitro liver enzyme activity associated with glycerol production

Lewis, Johanne M. (2002) Freeze resistance in rainbow smelt (Osmerus mordax) : seasonal patterns of glycerol and antifreeze protein accumulation and the in vitro liver enzyme activity associated with glycerol production. Masters thesis, Memorial University of Newfoundland.

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Abstract

Rainbow smelt (Osmerus mordax) inhabit inshore waters along the North American Atlantic coast. During the winter, these waters are frequently ice covered and can reach temperatures as low as -1.9°C. The freezing point of normal teleost blood is between -0.7 and -0.9°C. Therefore, to prevent freezing, smelt accumulate antifreeze proteins (AFP) and high levels of glycerol, which, unlike AFPs, lower the freezing point via colligative means. By performing a long term acclimation study, it was discovered that the upregulation of the antifreeze response (both glycerol and AFP) occurs in early fall, when water temperatures are 5-6°C. The accumulation of glycerol appears to be the main mechanism of freeze resistance in smelt as it contributes more to the lowering of the body's freezing point than the activity of the AFP (0.4 - 0.5°C versus 0.3°C for glycerol and AFP, respectively). The role of the AFP appears to be a safeguard mechanism to prevent freezing when glycerol levels are low. The significant increases in activities of the liver enzymes GPDH, AlaAT and PEPCK and their significant correlations with increasing glycerol levels, indicate that these enzymes are closely associated with, but do not regulate, the synthesis and maintenance of elevated glycerol levels in smelt for use as an antifreeze.

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