Variability in brain ganglioside composition: A further molecular mechanism beside serum antifreeze-glykoproteins for adaptation to cold in Antarctic and Arctic-boreal fishes

Abstract

Gangliosides and sialoglycoproteins from brain, liver and muscle have been isolated from 6 Antarctic fish species from the suborder Notothenoids and from 4 Arctic-boreal fish species. In addition freezing and melting points from serum of both groups were examined in order to determine the presence of protein antifreezes. In comparison with eurythermic fishes of temperate climates in both groups the phylogenetical adaptation to cold is correlated with a significantly higher concentration of gangliosides in the brain. The ganglioside concentration of liver in Antarctic fish, but not in Arctic species, is 3 to 5fold higher than in mammals (rat); in muscle the ganglioside content is increased only in red-blooded Antarctic fish as compared with mammals. The concentration of neuronal sialo-glycoproteins generally is lower in Antarctic fish than in other marine teleosts; in muscles the content is 2 to 3fold higher than in mammals. The molecular composition of brain gangliosides is characterized by an extreme high polarity which is due to an equipment with highly sialylated fractions (40 to 50% higher sialylated than tetrasialogangliosides). There are distinct differences between the freezing and melting point of blood serum, especially in the Antarctic species in favour of the existence of protein antifreezes. The results are discussed with regard to the fact that the extremely high polarity of brain gangliosides reflects a very efficient mechanism on molecular level to keep the neuronal membrane functional under low temperature conditions.