Kinetic and Thermodynamic Characteristics of Lactate Dehydrogenase in Skeletal Muscles of Homeo- and Heterothermic Animals at Low Body Temperatures

Resumo

Kinetic and thermodynamic characteristics of lactate dehydrogenase (LDG) in skeletal muscles were analyzed in homeothermic animals (rats) under deep (20°C) artificial hypothermia and in heterothermic animals (ground squirrels) under natural hypothermia (hibernation). It was found that, despite different etiology of hypothermic states, changes in some LDG parameters both in homeo- and heterothermic animals at low body temperatures are unidirectional: the catalytic efficiency decreases, the optimum point on the concentration curve shifts towards higher concentrations, efficient activation energies and K_i values increase. At the same time, multidirectional changes in LDG V_max and K_M values as well as the degree of their manifestation in rats versus ground squirrels at low body temperatures indicate that the mechanisms, which regulate activity of this enzyme in animals with diverse strategies of thermal adaptation, are quite different.