Thermal stability of molecular forms of acetylcholinesterase from muscle microsomes

To establish if the predominant form of acetylcholinesterase in muscle microsomes (4.8S) corresponded to the monomeric or dimeric form of the enzyme we studied the sensitivity to heating of Triton X-100 solubilized extract and that of 4.8S, 10-11S and 13.5S species of the enzyme. Inactivation of soluble acetylcholinesterase began at 45-47 degrees C and was almost complete at 60 degrees C. Sedimentation analysis revealed that the partial loss of activity was due to inactivation of the 4.8S form, although by heating the 13.5S was converted into the 10S enzyme. Inactivation of the 4.8S form began at 45 degrees C, whereas the larger forms required higher temperature. The 4.8S component follows a time course of inactivation which could be fitted by a double exponential equation (when heated at 52 degrees C, almost 83% of the activity showed a short half-life). The 10-11S species was also inactivated following a two step process while the 13.5S enzyme was fairly stable at 52 degrees C. The results show that the lightest component behaves as a monomeric form of acetylcholinesterase.