The kinetic and thermodynamic characteristics of lactate dehydrogenase in the rat brain during hypothermia

Abstract

We studied the activity and kinetic and thermodynamic characteristics of LDH in the rat brain during short-term and long-term (3 h) moderate (30°C) hypothermia and short-term deep (20°C) hypothermia. We found that a decrease in the body temperature of rats to 30°C resulted in an increase in the LDH activity and a shift in the optimum point on the plot of the concentration dependence in the direction of higher concentrations of pyruvate. Analysis of the kinetic characteristics of the enzyme during moderate hypothermia points to a pronounced increase in V_max and K_i, which was associated with an insignificant decrease in K_m; this increases the efficacy of enzymatic catalysis and decreases the extent of substrate inhibition. However, the character of the temperature dependence of LDH activity also changed, which was determined by a decrease in the effective energy of activation and enthalpy of activation. The above effects of shortterm moderate hypothermia during its prolongation became more pronounced. However, after deeper hypothermia, the LDH activity, character of its concentration and temperature dependence and kinetic and thermodynamic characteristics considerably did not differ from the control characteristics. The possible mechanisms and biological sense of the found changes in the kinetic and thermodynamic characteristics of LDH in the rat brain at low body temperatures are discussed.