Activation of choline acetyl transferase by dihydrolipoic acid.

In a previous article we present results that demonstrated that the enzyme, choline acetyl transferase, was strongly activated by dihydrolipoic acid and that the oxidized form of this substance, lipoic acid itself, was an inhibitor of the enzyme and overcame the stimulatory effects of reduced lipoic acid. The experiments presented in this article show that dialysis of a partially purified preparation of choline acetyl transferase causes complete disappearance of enzyme activity and that addition of dihydrolipoic acid restores activity towards normal. In addition we present experiments with extracts of rat brain and heart as well as rabbit bladder tissue. In these extracts dihydrolipoic acid strongly activates the enzyme. Dialysis of brain and heart extracts causes loss of activity with partial restoration of activity by addition of dihydrolipoic acid. Reduced glutathione has no ability to stimulate activity of the enzyme. We conclude that the results of these experiments strongly support the view that dihydrolipoic acid acts as a coenzyme in the choline acetyl transferase reaction.