Acetylcholine synthesizing enzymes in frog skeletal muscle.

Acetylcholine synthesis in homogenates of frog sartorius muscle was measured by a radiometric method with a low blank. Choline acetyltransferase activity was very low (Vmax, 2nmol . g-1 . h-1, Km for choline, approx. 50 microM). The enzyme was found only in the endplate area and disappeared after denervation; it was inactivated by 4-(1-naphthylvinyl)pyridine. At high substrate concentrations its activity was overshadowed by the acetylcholine-synthesizing activity of a different enzyme not saturated by 10 mM-choline. The non-specific enzyme was present at and away from the endplate area, and it was not affected by denervation.