Concentration of choline acetylase in conducting tissue

Abstract

In view of the recent information accumulated about the acetylating mechanism, choline acetylase activity has been redetermined in a few representative types of conducting tissue. This enzyme which specifically catalyzes the transfer of the acetyl group from acetyl-CoA to choline, is of great biological interest. Re-evaluation of its concentration under optimal experimental conditions, especially in the presence of a powerful activating system, appeared desirable. 1. 1. Extract from acetone-dried powder of guinea pig brain forms under optimal conditions 2.0–2.5 mg. acetylcholine/g./hr. The data are the same as reported previously without addition of the acetate activating enzyme system, thus indicating the presence of adequate amounts of the system in the preparation. 2. 2. In other tissues the concentrations expressed in milligrams acetylcholine formed/g./hr. were as follows: in peripheral nerve (rabbit sciatic) 1.3; in striated muscle (goldfish) 3.0–4.0; in electric tissue ( Electrophorus electricus) 0.36; in heart muscle (rabbit) 0.015–0.040. The value for electric tissue was obtained with extracts of fresh tissue, in the other cases with extracts of acetone-dried powder. 3. 3. A more detailed study was made of the enzyme activity in dorsal and ventral roots in view of reports that dorsal roots do not contain choline acetylase and the sweeping conclusions based on the failure to find enzyme activity. The enzyme is present in both types of fibers. In dorsal roots 12–20 μg. of acetylcholine are formed/g. fresh tissue/hr. In ventral roots the enzyme concentration is extraordinarily high, 2 mg./g./ hr. in those of ox and 5 mg./g./hr. in those of dog. The latter figure is higher than that found with squid head ganglia which so far had the highest concentration of choline acetylase observed. 4. 4. The ratio of concentration of acetylcholinesterase over choline acetylase was found to be in most cases several hundred to a thousand or more. An exception is the ventral roots, where the ratio is 6. 5. 5. Some physiological implications are discussed.