Thermal denaturation of acetylcholinesterase of brain synaptic membranes of ground squirrels in hibernation

We studied the thermal denaturation of acetylcholinesterase of brain synaptic membranes of ground squirrels (Spermophylus pigmaeus) in hibernation. We found that the enzyme activity increases during bouts of hibernation and decreases during interbout arousal. The kinetics of the enzyme denaturation at 48°C has two exponential stages, fast and slow, with rate constants of k1 = 0.376 min−1 and k2 = 0.040 min−1, respectively (for control animals in the summer period). The rate constants of denaturation decreased during bouts of deep hibernation and interbout arousal, as compared to the summer control. We discuss the possible mechanisms of changes in the enzymatic activity and thermostability of brain acetylcholinesterase during hibernation.