Some Effects of Salts on True Cholinesterase

Abstract

The activity-substrate conc. curves of true cholinesterase (TCh) were detd. in a medium containing 0.025 M NaHC03 and also in media with the alkali plus salts in varying concs. The enzyme activity was detd. manometrically at 37.5[degree]C. by Warburg''s method. TCh from the sera and parotid glands of ox and sheep, from mammal. erythrocytes and from brain tissue of any vertebrate, when measured in a medium containing no salts other than NaHCCO3, was subject to excess substrate inhibition and was most active at low acetylcholine concs. (0.00015 M-0.0005 M). Addition of salt to the medium changed the relation between enzyme activity and substrate conc. A stepwise increase in salt conc. (KC1) did not abolish the excess substrate inhibition, but shifted the optimal enzyme activity to higher levels of acetylcholine. An absolute increase in the rate of acetylcholine hydrolysis occurred at and beyond the new optimum levels. A similar though not identical trend was observed upon adding NaCl instead of KC1.