Acetylcholine formation in lobster sensory axons

• 1.

  1. The concentration of choline acetylase (acetyl-CoA: choline O-acetyltransferase, EC 2.3.1.6) in the nerve fibers of the walking leg of the lobster has been determined. In sensory bundles, dissected from the whole nerve trunk, the activity of the enzyme was found to be on the average 2 μm/g wet wt./h; the values of the whole nerve' trunk were similar.

• 2.

  2. The sensory bundle is formed by approx. 800 axons, each about 5 μ in diameter, estimated on the basis of photomicrographs; the total surface area per g nerve is therefore approx. 400 cm². Referred to cm³/sec the enzyme activity amounts to 1.5·10⁻⁶ μm of acetylcholine formed.

• 3.

  3. Recent information on the concentration of acetylcholinesterase (acetylcholine acetyl-hydrolase, EC 3.1.1.7) in lobster nerves per unit time and surface area permits an estimate of the amount of acetylcholine which may be hydrolyzed per cm². On this basis the amount of acetylcholine formed in the sensory axons would be adequate for more than 400 000 impulses/h.

• 4.

  4. The objection was raised to the proposal role of acetylcholine in conduction, that the concentration of choline acetylase in sensory fibers is too low to be compatible with the theory. This difficulty has now been eliminated.