BENZOYLCHOLINE AND ATROPINE ESTERASES

¹ From the Department of Physiology and Pharmacology Duke University School of Medicine, Durham, North Carolina

1. The plasmas (and also livers and kidneys) of rabbits show great individual variation in their ability to hydrolyze benzoylcholine. This activity may be completely lacking from some plasmas.

2. The activities of the rabbit plasmas on benzoylcholine bear a general, though not quantitative, proportionality to their activities on atropine.

3. The distribution of benzoylcholine esterase and atropine esterase in the tissues of rabbits, guinea pigs and frogs are quite different. Rabbit livers and plasmas have either both activities or neither one; guinea pig livers have only the former; whereas frog livers have essentially only the latter.

4. Benzoylcholine esterase is more sensitive to both neostigmine and fluoride inhibition than is atropine esterase.

5. Incubation of rabbit liver globulin at 48°C. for a sufficient length of time produces a benzoylcholine esterase preparation free of atropine esterase activity.

6. Benzoylcholine esterase and atropine esterase are distinct and separable entities.

7. Benzoylcholine esterase has a low dissociation constant for its substrate (K_a, about 0.002). The dissociation constant for pseudo-choilnesterase and benzoylcholine is much less than 0.0003.