THERMAL METABOLIC ADAPTATIONS IN POIKILOTHERMS AT VARIOUS STAGES OF ONTOGENY BY THE EXAMPLE OF CARBON METABOLISM ENZYMES

Functional properties of enzymes of poikilotherms at various stages of ontogenesis above all depend on the temperature of the species habitat and is also influenced by acclimation temperature. The relationship has been shown between the temperature of fish development and the minimal Michaelis constant (K(m)) for lactate dehydrogenase and glucose-6-phosphate dehydrogenase in embryos of rainbow trout, least cisco, Arctic cisco, loach, carp, goldfish, and danio. Adaptation of kinetic properties of embryonic lactate dehydrogenase to various temperatures takes place for 15-20 days as established for trout, while shorter thermal influences had no effect on the thermal minimum of K(m). By contrast, kinetic properties of lactate dehydrogenase changes much faster (for 36-40 h) during the loach oocytes maturation. Fish acclimation to low and high temperatures changes the minimal K(m) for lactate dehydrogenase and glucose-6-phosphate dehydrogenase to low and high temperatures, respectively. The range of these changes is wider for lactate dehydrogenase than that for glucose-6-phosphate dehydrogenase. Lactate dehydrogenase isolated from skeletal muscles of loach acclimated to low temperature has higher specific activity and is more resistant to thermal and urea inactivation.