Turnover of the Molecular Forms of Acetylcholinesterase in the Rat Diaphragm

Abstract: The turnover of acetylcholinesterase (AChE) and its molecular forms was measured by following the loss of enzyme activity in the right hemidiaphragms of Sprague-Dawley rats treated with cycloheximide, 20 mg/kg, every 4 h. This treatment inhibited 96% of the incorporation of [³H]leucine into muscle protein. After 8 h of treatment, the total AChE activity of the diaphragm decreased by 17% ( P < 0.01). Assuming first-order exponential kinetics, a half-life of 30 h and an hourly turnover of 180 units were calculated. The measured accumulation of AChE activity at a ligature on the phrenic nerve indicated that axonal transport contributed trivially to this turnover. Sucrose density gradient experiments showed that the cycloheximide-induced loss of AChE activity was restricted to the 4S enzyme, which had an apparent half-life of 6.2 h.