Abstract– We have solubilized three active molecular forms of AChE from rat muscle and have confirmed the presence of one of these forms (EP form, apparent sedimentation coefficient: 16 s) uniquely at the motor end-plate regions of several skeletal muscles. This form was never detected in smooth muscle extracts. In sternocleidomastoïdian muscle it disappeared after denervation and reappeared after re-innervation in the region where nerve and muscle had come in contact. During the embryonic development of hind leg muscles the EP form appeared on the 14th or 15th day of gestation.

The EP form of muscle AchE appears to be an excellent biochemical marker of the neuromuscular junction.