Turnover of the molecular forms of acetylcholinesterase in the rat diaphragm

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 less than 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 low of AChE activity was restricted to the 4S enzyme, which had an apparent half-life of 6.2 h.