Hydrolysis of Acetycholine by Turtle Blood. ∗

Abstract

In connection with studies being conducted in this laboratory on the physiology of the turtle heart, it was of interest to know the choline-esterase activity of turtle blood. Work already done on the blood of other forms has revealed marked differences in the hydrolysis of acetylcholine between whole blood and serum and further variations depending upon the species. Galehr and Platt-ner 1 , 2 found that human whole blood, shadow cells and washed corpuscles have a greater hydrolytic action on acetylcholine than the serum has. The filtrate from an acetylcholine solution treated with animal charcoal was from 78-100% physiologically inactive, but the total activity could usually be restored by acetylation. By analogy to the charcoal effects they concluded that the hydrolysis of acetylcholine by blood was due to surface catalysis. On the other hand, Engelhart and Loewi 3 repeated the charcoal experiments of Galehr and Plattner and found that partial inhibition of the destruction of acetylcholine could be obtained with a 1:5,000 dilution of physostigmine, which had been shown to be effective in preventing acetylcholine hydrolysis by extracts of frog hearts, and complete inhibition with equimolar concentrations of strychnine. They showed that physostigmine also completely prevented this hydrolysis by defibrinated beef blood in much greater dilutions (1:30,000) and by human serum in dilutions as great as 1:400,000. Strychnine did not have this effect on blood. When beef blood was heated at 58°C its hydrolytic activity was lost while human blood retained its activity when treated in the same manner. However, it was shown that although dried human blood retained its hydrolytic activity, it was lost after heating at 58°C. On the basis of these results, they concluded that the acetylcholine-splitting activity of human and beef sera, plasma, erythrocytes and stromata is due to the presence of an enzyme rather than to surface catalysis, and that this enzyme is not necessarily different in beef and human blood since drying of the blood might inactivate a protective agent.