Abstract
Cholinesterase activities (ChE) with various substrates and in the presence and absence of inhibitors were measured in sera from human and animals, and the following results were obtained.
1. True ChE, which is inhibited by caffeine but not ethopropazine with acetylthiocholine as substrate, was present to a greater extent in animals than in human. Differences of the inhibition by caffeine and ethopropazine suggest that proportions of true ChE to total ChE were about 60% in rabbits, 40% in male rats, 16% in dogs, 10% in monkeys and 7% in human.
2. In rabbits, some (type I) hydrolysed butyrylthiocholine to a significantly higher extent than others (type II). Since this hydrolysis was mostly inhibited by DFP but hardly inhibited by EDTA or eserine, it was probably due to carboxyesterase.
3. In female rats, ChE with acetylthiocholine as substrate showed age-dependent differences in activity, Km value, and inhibtions by caffeine and ethopropazine. True ChE was constant regardless of age, indicating that the differences were due to the change of pseudo-ChE.
