THE ACTIVITY OF AN ENDOPLASMIC RETICULUM-LOCALIZED POOL OF ACETYLCHOLINESTERASE IS MODULATED BY HEAT-SHOCK

Primary cultures prepared from embryonic chick pectoral muscle were su bjected to heat shock, and the effect on acetylcholinesterase activity in the cultures was examined. A rapid recovery in enzyme activity was observed soon after an initial heat shock-induced drop and was shown to be independent of de novo synthesis of protein, since it could occu r in the presence of an inhibitor of protein synthesis. Lectin binding and sucrose gradient centrifugation studies suggested that molecular monomers and dimers found in the endoplasmic reticulum are involved in the observed recovery of acetylcholinesterase activity. Enhanced acti vation of a preexisting pool of inactive enzyme was clearly not the ma in agent of the recovery in enzymic activity. Recovery relied principa lly on restoration of the activity of previously active, heat-denature d acetylcholinesterase molecules found in the endoplasmic reticulum. P ossible agents involved in the recovery of enzymatic activity might be heat shock proteins acting as molecular chaperones.