The Kinetics of Thermal Denaturation of Acetylcholinesterase of the Rat Red Blood Cell Membrane during Moderate Hypothermia

Abstract

The thermostability of acetylcholinesterase of rat erythrocyte membranes in the norm and moderate hypothermia was studied. It is shown that the kinetics of the thermal denaturation of acetylcholinesterase is nonlinear and corresponds to a model that involves two-step denaturation, fast and slow, of the enzyme’s native form. The rate constants of the fast phase, k₁, are much higher than those of the slow phase, k₂, while the energy of the fast phase activation is lower by only 19.4% compared to that of the slow one. Short-term moderate hypothermia is shown to increase k₁ and decrease the index of relative activity of the intermediate form of acetylcholinesterase (parameter β), leading to significant lowering of the activation energies of both stages; parameter β becomes more temperature dependent. The prolongation of hypothermia up to 3 h mainly contributes to a decrease in k₁ and k₂ relative to short-term hypothermia and the activation energy of denaturation increases. These data support the hypothesis according to which the structure of acetylcholinesterase is labilized at the initial stages of the development of the hypothermic state and stabilized during prolonged hypothermia.